1995 altima slow idle question(s)

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  #1  
Old 09-09-10, 06:37 AM
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1995 altima slow idle question(s)

My old car has 200k and a slow idle issue.
It idles a bit irratically at stop lights about half the time--meaning the idle goes up and down some or is a bit suppressed (450-600 rpm or so). Seems to happen less when the car is warm, but no true consistentcy to occurances.
If the AC is on then the slow idle is about 800 or so and the prob. happens less often.
When the car is moving it seems fine. Might rule out fuel filter

Changed valve cover gasket b/c of leaky spark plug seal and all plugs looked ok, not fouled etc. . . .
Believe I have a knock sensor code stored and check engine light has lit and gone off and lit again b/c of it.
At $140 I an not running out to replace the sensor until I am sure.
Will check to make sure the sensor is not loose this weekend.

Also told one oxy sensor is running rich and the other lean, can I warranty them because of that??--neighbor has a high dollar code readers--need to call him.

Any help is, as always, much appreciated.
 
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  #2  
Old 09-09-10, 02:09 PM
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Rule out:

Vacuum leaks
Exhaust leaks
Air leaks



Test the “IAC” as below.

Disconnect the electrical harness from the valve.

Measure the resistance between the illustrated connector terminals.

Resistance should be 10 ohms @ 77°F (25°C).
If resistance is not within specification, the valve may be faulty.

If resistance is within specification, check the circuits back to the ECM



Test “MAF” as below.

Using a multimeter, check for voltage by backprobing the MAF sensor connector.

With the ignition switch ON and the engine stopped, voltage should be less than 1.0 volt.

With the engine idling at operating temperature, voltage should be 1.3 -1.7 volts.

With the engine running at approximately 4000 rpm, voltage should be approximately 4.0 volts. Try cleaning the “MAF”. Use only “CRC MAF” cleaner, and follow the cleaning instructions on the can exactly. Be careful not to touch the contacts on “MAF” with your fingers or rag. The contacts are delicate and can be sasiely damaged if touched.

It is important to watch for a linear voltage rise in response to increases in engine rpm, up to about 4000 rpm.

If voltage is not within specifications, check the power and ground circuits, the MAF sensor may be faulty.


Testing “Front” O2 Sensor

Disconnect the sensor electrical harness.

Measure resistance between the outer terminals of the connector.

Resistance should be 2.3-4.3 ohms @ 77°F (25°C).

Check continuity between the center terminal and each of the outer terminals. Continuity should not exist.

If resistance is not as specified or continuity exists, the oxygen sensor is faulty.

If resistance and continuity are within specification, check and repair the circuits.

Testing “Rear” O2 Sensor

Disconnect the sensor electrical harness.

On models with a three-terminal connector, measure resistance between the two outer terminals. On models with a four-terminal connector, measure resistance between the two illustrated terminals.

For three-terminal connectors, the resistance should be 5.2-8.2 ohms @ 77°F (25°C). For four-terminal connectors, the resistance should be 2.3-4.3 ohms @ 77°F (25°C).

On models with a four-terminal connector, also check continuity between the various terminal combinations.

Continuity should not exist.

If resistance is not as specified or continuity exists, the oxygen sensor is faulty.

If resistance and continuity are within specification, check and repair the circuits.


Reading error codes

Remove the access cover and locate the mode adjusting screw and LED on the ECM.

Turn the ignition switch ON , but do not start the engine. Both the LED and the malfunction indicator lamp on the instrument panel should be illuminated. This is a bulb check.

Start the engine.

Switching modes is not possible while the engine is running.

If the LED or malfunction indicator lamp illuminates, there is a fault in the system.

Turn the mode selector screw fully clockwise. Wait 2 seconds, then turn the screw fully counterclockwise.

The diagnostic trouble codes will now be read from the ECM memory. They will appear as flashes of the malfunction indicator lamp, or the ECM's LED.

After all codes have been read, turn the mode selector screw fully clockwise to erase the codes.

Turn the mode adjusting screw to the fully counterclockwise position whenever the vehicle is in use.

Turn the ignition OFF .

When the ignition switch is turned OFF during diagnosis, power to the ECM will drop after approximately 5 seconds. The diagnosis will automatically return to Mode 1 at this time.

Clearing codes

The easiest way to clear trouble codes is to turn the mode selector screw fully clockwise after all codes have been read.
Turn the mode adjusting screw to the fully counterclockwise position whenever the vehicle is in use. The diagnostic memory will also be erased if the negative battery terminal is disconnected for 24 hours.

“TPS” test will follow shortly.
 
  #3  
Old 09-09-10, 05:52 PM
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Idle is controlled by the IAC valve. Idle speed is increased by the IAC valve when you turn on the A/C, so sounds like the IAC is working.

The IAC lets in more or less air and can become clogged. Might try cleaning the IAC air openings and pintle with throttle body cleaner.

Also idle air gets in through the PCV valve. That and its associated hoses can become clogged with crud. Clean those out so air can flow.

Other than that, be sure to do all the regular recommended maintenance as listed in your owner's manual for various mileage intervals. Change air/oil/fuel filters, oil, spark plugs, spark plug wires, distributor cap and rotor (if you have those), etc.

Be sure to replace with factory specification parts only as recommended by your owners manual.
 
  #4  
Old 09-10-10, 06:31 PM
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Throttle closed-approximately 1 kilohm

Throttle partially open-1-10 kilohms

Throttle fully open-approximately 10 kilohms

Slowly rotate the throttle shaft and monitor the ohmmeter for a continuous, steady change in resistance.

Any sudden jumps, or irregularities in resistance (such as jumping back and forth), indicates a malfunctioning sensor.

Do not perform this test on the electrical harness connector terminals, but rather on the terminals of the sensor itself.

If resistance is not within specification, the sensor may be faulty.

If resistance is within specification, check the circuits back to the ECM.

Connect the electrical harness to the sensor.


Position Switches

Disconnect the electrical harness from the sensor.

Check continuity between the connector terminals.

When the throttle is placed in the appropriate position (idle or wide open throttle), continuity should exist.

When the throttle is not in the idle or wide open throttle position, continuity should not exist.

The position switches are an integral part of the TP sensor and cannot be replaced separately. If faulty, the TP sensor must be replaced as an assembly.

If continuity is not as specified, the sensor is faulty.
 
  #5  
Old 09-10-10, 07:09 PM
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Thanx for the Info.!
Lots to look at tomorrow
 
  #6  
Old 09-10-10, 07:57 PM
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You’re welcome. No problem. Just keep in touch with us and tell us your findings.

(Quote) neighbor has a high dollar code readers

That’s why I posted all the information I did. It may seem like a lot and complicated, but it really is easy and straight forward. The fact that your neighbor has “High Dollar” tools tells me that he most likely has the skill and knowledge to use those tools. He should be able to help you and interpret the information I posted.
 
  #7  
Old 09-11-10, 09:23 AM
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Collant temp. sensor location???

One more quick question: Any idea where the coolant temp. sensor is?? Not the temp. sending unit for the dash guage, but the actual temp. sensor. I haven't looked close in the engine for it yet--but my haynes manual only mentions the sensor in their OBD-II trouble code list for 1998 and later--no componet check or location.

I found an altima forum for my uears and there were some posts regarding the sensor. Seems like an idea to pull it and clean it. had a prob. once with a neon and it was the sensor throwing off other codes.

Thanx again
 
  #8  
Old 09-11-10, 04:01 PM
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I don't know where it is...

That is one reason I like a Factory Service Manual set of books (many times 4 books) which you can order from your dealer.

That would show the location and would also give testing instructions. That would measure a certain resistance at a certain temperature using a multimeter.

Then you can test these things and not replace them if they are working ok. Otherwise you are just guessing.
 
  #9  
Old 09-11-10, 05:12 PM
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(Question) Any idea where the coolant temp. sensor is??

Center, upper (part) engine area, mounted on top front passenger side of engine. (Image at bottom of page). Test to follow..

Pull it, clean it, test it, sleep with it if you want, but don’t change it until you check it and it proves defective. Very rare that the temp sensor is causing your problem, but slim possibility exists. Still waiting for error codes. See “Reading Codes” from info posted yesterday. Scan tool is not needed to read codes. Here’s more.


Turn ignition On.

Turn diagnostic mode selector on ECU fully clockwise and wait until inspection lamps flash. Number of flashes displayed indicates corresponding mode.

Note number of flashes, then immediately turn diagnostic mode selector fully counterclockwise.

If ignition is turned Off during diagnosis, in each mode, and then turned back on again after power to the ECU has dropped off completely, diagnosis will automatically return to


Mode I.

For description of modes, proceed as follows:

(Mode I): with engine stopped, system in bulb check state. with engine running, system in malfunction warning state.

(Mode II): with engine stopped, system in self diagnostic results state. with engine running, system in front O2S monitor state.

11 Crank Angle Sensor/Camshaft Position Sensor.
12 Air Flow Meter/Mass Air Flow Sensor.
13 Engine Coolant Temperature Sensor.
14 Vehicle Speed Sensor.
21 Ignition Signal.
22 Fuel Pump.
23 Idle Switch.
24 Throttle Valve Switch.
25 Idle Speed Control Valve.
28 Cooling Fan Circuit.
31 ECM.
32 EGR Function.
33 Heated Oxygen Sensor.
34 Knock Sensor.
35 Exhaust Gas Temperature Sensor.
36 EGR Control-Back Pressure Transducer.
37 Knock Sensor.
38 Right hand bank Closed Loop (B2).
41 Intake Air Temperature Sensor.
42 Fuel Temperature Sensor.
43 Throttle Position Sensor.
45 Injector Leak.
47 Crankshaft Position Sensor.
51 Injector Circuit.
53 Oxygen Sensor.
54 A/T Control.
55 No Malfunction.
63 No. 6 Cylinder Misfire.
64 No. 5 Cylinder Misfire.
65 No. 4 Cylinder Misfire.
66 No. 3 Cylinder Misfire.
67 No. 2 Cylinder Misfire.
68 No. 1 Cylinder Misfire.
71 Random Misfire.
72 TWC Function right hand bank.
73 TWC Function right hand bank.
76 Fuel Injection System Function right hand bank.
77 Rear Heated Oxygen Sensor Circuit.
82 Crankshaft Position Sensor.
84 A/T Diagnosis Communication Line.
85 VTC Solenoid Valve Circuit.
86 Fuel Injection System Function right hand bank.
87 Canister Control Solenoid Valve Circuit.

91 Front Heated Oxygen Sensor Heater Circuit right hand bank.

94 TCC Solenoid Valve.
95 Crankshaft Position Sensor.
98 Engine Coolant Temperature Sensor.

101 Front Heated Oxygen Sensor Heater Circuit right hand bank.

103 Park/Neutral Position Switch Circuit.
105 EGR and EGR Canister Control Solenoid Valve Circuit.
108 Canister Purge Control Valve Circuit



 
  #10  
Old 09-11-10, 06:04 PM
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Coolant Temp Sensor Test.







Disconnect the engine electrical harness from the ECT sensor.

Connect an ohmmeter between the ECT sensor terminals.

With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.

Connect the engine electrical harness to the sensor.

Start the engine and allow it to reach normal operating temperature.

Once the engine has reached normal operating temperature, turn it OFF .

Once again, disconnect the engine electrical harness from the ECT sensor.

Measure and note the ECT sensor resistance with the engine hot.

Compare the cold and hot ECT sensor resistance measurements with the accompanying chart.

If readings do not approximate those in the chart, the sensor may be faulty.
 
  #11  
Old 09-12-10, 06:31 PM
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Ok, update time.
Spent some time this weekend playing with this old car.

I've changed out coolant temp. sensor--old one probably was ok but have had issues in past with them in other cars so what the hey--it was original equipment, maybe.

Bought MAF sensor cleaner and used it gently.
A couple of years back I had the distributor replaced and then a dirty MAF sensor mimiced the symptoms of the oil-clogged distributor. The mechanic who did the distrib. told me this and cleaned the MAF for free. Car would stall and have to be restarted when distrib. was bad and when MAF was dirty so cleaning with something more than canned air seemed a decent idea.

Bought throttle/choke cleaner and cleaned throttle body on the inside. Did it help, who knows--couldn't hurt I thought.

Bought new fuel filter and changed it out--yes the fuel that drained out from the "in" side was pretty dirty. Good move to change it out I thought.

Replaced distributor cap and rotor--this car can go through those and the idle is effected when they have had enough. I warrantied these out so there were free
These two probably were the most responsible for idle issues.

Cleaned some battery connections.

Checked coil resistances.

Cleaned sparkplug wire connections where they met the new distributor cap.

Tested coil wire resistance.

Tested upstream oxy sensor voltage. Voltage was on the money before starting, but my manual said the voltage should increase and vary when car is warmed up. But on mine the voltage went down to almost zero. This one I am confused about. I have not yet checked the code stored in the system but the car seems ok. If the oxy sensor was bad I think I would notice something, well at least I hope so. then again incorrect voltage to the sensor may not be the fault of the sensor.

I think that's all I did and the idle seems smoother, but is now higher than normal. I haven't driven it for more that 3-4minutes at slow speeds so I will see what happens tomorrow.
But it seems better otherwise.

My car doesn't have the blinking code checker thingee I can use a screwdriver on. Well, it has it but it is not functional. There is no bulb or screw to turn. I tried that a few years ago and found it to be non-functional as I recall. So the multi-pin connector under the dash by the fuse panel inside is how I check the codes.

Thanx for all the help and I hope all we put on these posts can help someone else with their car.

Can't wait to get a newer car WITHOUT A DISTRIBUTOR CAP AND ROTOR. a major souce of issues for me over the last few years.
 
  #12  
Old 09-12-10, 07:23 PM
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[QUOTE=cbuddy2005;1766735]My old car has 200k and a slow idle issue.
It idles a bit irratically at stop lights about half the time--meaning the idle goes up and down some or is a bit suppressed (450-600 rpm or so).

I can't help but think there may be carbon in the EGR valve holding it open @ times (if you have one) but I'm not too familliar with these, Just throwing an Idea out for you,,, Roger
 
  #13  
Old 09-13-10, 05:16 AM
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Yes, I have thought of that also. Had to special order the gasket for the connection where it bolts on, so I have yet to pull it just to check.

I just know it can't be that because it's too easy to reach on the car--right on top.

Thanx
 
  #14  
Old 09-13-10, 05:47 AM
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(Quote) Tested upstream oxy sensor voltage. Voltage was on the money before starting, but my manual said the voltage should increase and vary when car is warmed up. But on mine the voltage went down to almost zero.

There are a significant number of reasons for this. I never guess at a problem, and I never haphazardly change parts in an effort to resolve a problem. I treat the vehicle problems on this forum as if they mine. You should know that your Altima has a “Downstream” O2 sensor as well. I would have to see:

The test results from both sensors
Under the proper driving conditions
And at the proper engine operating temperatures


To determine why your voltage reading went down to zero. Individuals who tell you; “That the O2 sensor is bad, or say that the sensors “Heater Circuit” is open or shorted are just guessing. It’s not fair to guess with another person’s money. A part must never be changed until it is checked and found to be defective.

(Quote) This one I am confused about. I have not yet checked the code stored in the system but the car seems ok. If the oxy sensor was bad I think I would notice something.

Not necessary and not always. Many times there will be no drive ability or performance issues to speak of.

(Quote) My car doesn't have the blinking code checker thingee I can use a screwdriver on. Well, it has it but it is not functional. There is no bulb or screw to turn. So the multi-pin connector under the dash by the fuse panel inside is how I check the codes.


1995 was the conversion year. In other words, 1995 was the year that vehicle manufacturers started converting OBD I systems over to OBD II systems. By 1996 all diagnostics were OBD II. Actually, since you car has the diagnostic link under the dashboard, it means that your car is an “Early Production” 1996 Altima that was manufactured in late 1995. Auto Zone reads car computer codes for free, on vehicles from 1996 and up. Go to an Auto Zone store, and have that stored code read, and post it here for us to see. Don’t be surprised if you have more than one code.
 
  #15  
Old 09-13-10, 06:41 AM
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One more bit of info. I witnessed this am.
car sat overnight and after letting fuel pump run for a second the car fired right up.

It used to take car a half-second or so to fire up after priming the fuel system having sat the night. Sunsequent starts would happen faster after the initial one.

Just something I noticed. Have not yet tested the fuel pressure, but the new fuel filter may have something to do with it.

I have suspected the fuel pressure regulator for a long time, but I don't have any evidence to warranty replacing it.

Anyway, the car seems smoother now it just idles a bit higher than it should. I will drive it a while and see what happens.
I am not a person to start replacing parts without reason (excepting the coolant sensor)and chasing guesses on an old car. car is fragile in my opinion and messing around too much may result in busted plastic electric connectors etc. . .and even more issues than were there before.
Trying to keep the car safe and running until $$ for next one is available.

Will get codes read tonight.

Thanx all
 
  #16  
Old 09-13-10, 09:21 AM
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As to fixing things and your mention of buying another car, that is a financial decision.

The way I look at it, it is less expensive to fix my vehicles than to buy new vehicles. No matter what I need to do including replacing the engine/transmission.

$2000 is a LOT less expensive than $20,000 is the way I look at it!

So long as I can get parts, I'll keep the vehicle.

With that said, replacing the oxygen sensors will give you better gas mileage. These pay for themselves.

And for the fuel/starting issue, there is a one way "check valve" on the fuel system which keeps the fuel pressurized after the vehicle is turned off. Usually this is a part of the fuel pump. You can test these with a fuel pressure gauge. Turn the engine off, then wait about 30 minutes and the fuel pressure should be the same.

But if I was going to buy a new car, I don't think I would fix either of the above.
 
  #17  
Old 09-13-10, 02:16 PM
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cbuddy2005,

(Quote) car sat overnight and after letting fuel pump run for a second the car fired right up.

(Quote) It used to take car a half-second or so to fire up after priming the fuel system having sat the night. Sunsequent starts would happen faster after the initial one.

One second is good. Half as second is obviously better. Means “Static” fuel psi is holding and “Residual” is not “Bleeding Down”.

Keep an eye on it. If the cranking time becomes longer or extended, let us know. That’s a sign that residual fuel line pressure is being lost. The most common reason for that is a defective “Check Valve” at the fuel pump. New fuel filter has nothing to due with it. Age of car and mileage does.

(Quote) I have suspected the fuel pressure regulator for a long time, but I don't have any evidence to warranty replacing it.

Pull the vacuum hose at the fuel pressure regulator. If fuel is present inside the hose it means that the diaphragm inside the regulator is fractured, and the regulator must be replaced. Check back in about 3 hours. By then I have posted ‘Fuel Pressure PSI” stats.
 
  #18  
Old 09-13-10, 07:47 PM
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cbuddy2005,

Fuel pressure PSI values for your car.

Without vacuum applied to fuel pressure regulator. (43 PSI)

With vacuum applied to fuel pressure regulator. (34 PSI)


“Static” fuel pressure (KOEO) is (34 PSI). Pressure should come up quickly and hold steady. Shouldn’t drop off immediately. If drops off immediately, “Check Valve’ at fuel pump is failing.


Try below and let us know if you see a difference.

For the next few weeks keep the fuel tank full with a quality “Top Tier Fuel”. Don’t let the level go below half, and drive the car at 60mph four times a week.
 
  #19  
Old 09-14-10, 06:18 AM
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I would be buying another used Altima in cash no payments, something with a newer ignition system than the one I have now--the one I have has truly been around the block a lot of times. It is getting old all over.

Now for the-testing-the-fuel-pressure questions. From what I can tell the vacuum line is the one on top of the regulator, not the bigger line that is hose-clamped/directly connected to the fuel filter? Makes sense that the vacuum line is such but it never hurts to ask.

Also, I have no relief valve for the fuel line so for me to test the fuel pressure I would hook up a gauge that allows fuel to flow through it. And I would hook up this gauge on the fuel line closer to the filter or closer to the regulator or does that not matter?

And, since I have to interrupt the fuel line I would loose all pressure. When I hook the gauge in and turn the key on, but not start, the pump whirrs, should I then see an increase in pressure? Or does all the air in front of the incoming fuel have to be sucked out of the way by the vacuum when the enigne cranks/starts before I notice a pressure increase?

Then with the car running I remove the vacuum line from the regulator to check for a change in pressure? And why without vacuum does the psi value increase? Pump working
harder?

After I get my test values I would shut the car off and watch the gauge to see a possible decrease in psi and how rapid?

Sounds pretty basic but more experienced folks always have things to look for that others would miss.

Thanx for the advice--gotta' go find a gauge, any leads on a not too expensive one? Do parts stores lend them?
 
  #20  
Old 09-14-10, 11:20 AM
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cbuddy2005,

Of the stores below;

Auto Zone
Advance Auto Parts
O’Reilly Auto Parts

Have my own pro tools, and never shop in any of the above mentioned stores. Don’t know which (if any) are still loaning out diagnostic tools. You have to make some phone calls. Also check with private auto part stores (non chain). There are some that loan tools for free.

Auto Zone is only good for pulling codes and posting links.

You should never buy parts from them.


Click on link below.

| Repair Guides | Gasoline Fuel Injection System | Fuel Pump | AutoZone.com
 
  #21  
Old 10-03-10, 09:42 PM
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96 Altima with Problems

ASE MASTER

Just thought I could get your attention and ask you a few questions about my 96 Altima with 240K. I have hesitation and stalling that gets worse when the engine is hot. It it worst when I try to accelerate from stop and seems to go away at higher RPM. For the most part it idles in neutral fine and dies only on occasion when idling in drive or reverse. It is harder to start and sometimes requires I open the throttle to get it started again.

It is running lean, I know this by using the ECM Mode II diagnostic mode that shows the front O2 sensor status using the CEL. On = lean, off = rich. It hesitates wants to stall and has loss of power and the CEL indicates a lean condition when this occurs. If I pull the MAF the hesitation and stalling go away and it just has the 2.5K RPM limit due to limp mode (limits fuel). But I checked the voltage out of the MAF at idle and increased RPMs and it checks fine. I think this is because limp mode (fail-safe) dumps more gas into the cylinders(twice per engine cycle on all cylinders). The only codes it has are P0136 (O2 Bank 1 Sensor 2 low voltage) and P0325 (Knock Sensor). I think the rear O2 is due to damage from running over a truck tire on the highway, but regardless the ECM doesn't use it to control the engine.

I checked the fuel pressure and thought I had a bad regulator as it would not hold pressure with the ignition off sometimes so I replaced it. It holds pressure but I still have the problem. I also replaced the O2 sensor thinking maybe it was giving a faulty response (also it has at least 170K miles on it so for $17 why not, its a 1 wire). It didn't change anything.

I tested the EGR valve and the diaphragm moves freely. I also pulled vacuum from it and still it hesitates and stalls. There was a bad vacuum hose going to the EGR backpressure transducer so I replaced and no difference.

I know there is a problem with intake manifolds on altimas but I replaced mine about 2-3 years ago and the symptoms are completely different (rough idle, gets better at higher RPMs, rarely stalls).

I have reached the end of my abilities here and I have only two things left that I can try. About 6 months ago I was getting a misfire on cylinder 4 that went away with the EGR vacuum removed. Turned out the the manifold channels were filled with carbon so I cleaned it up and the problem went away. I didn't have a gasket at the time and just used high temp silicone to seal it. I am thinking maybe there is a leak there. However when I spray it with carb cleaner, the idle doesn't change. But I guess for $8 why not just rule that out. The last thing I want to try, due to cost is replace the MAF. I have cleaned it with spray but there is no difference. And as I mentioned it checked out with a volt meter and there are no codes for it but I figure it could be intermittent?

One last thing I for got to mention I checked the TPS and get 0.4V at idle and 4V WOT with even increasing resistance throughout the range . And I checked the ECT sensor, it was within range. Also I cleaned the camshaft sensor (LED encoder wheel) about 3 years ago and checked it now and it is clean.

Any thoughts would really help me out. Thanks!
 

Last edited by EZRydr; 10-03-10 at 11:37 PM. Reason: grammer
  #22  
Old 10-04-10, 07:21 AM
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Hmmm

I'm thinking a few things here.
* TPS might have a 'bad' spot in it. You said you checked it but was it a slow check to see the resistance doesn't have an erratic reading at any time while you moved it through its movement range?
* did you clean the inside of the throttle body? could be sticking a little bit
* slack throttle cable?
* clean/new fuel filter? if you change it put a cup to catch the fuel as it drains out from the bottom of the filter to see how much stuff is floating in the filter
* check inside condition of distributor cap terminals and the end of the rotor? a biggie for my altima!
* is there any leaking oil around/under your distributor cap? These cars are notorious for a leak fouling up the distributor function.
*I would check my plugs, wires, primary and secondary coil resistances


just a few thoughts
 
  #23  
Old 10-04-10, 11:20 AM
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EZRydr,

(Quote) Any thoughts would really help me out.

You’re making a classically typical mistake. You’re trying to resolve an issue in a car without resolving the issues that already exist. There’s a strong change if you resolve the issues that already exist that:

The hesitation and stalling that gets worse when the engine is hot will be resolved as well.

Start by making sure you resolve PO136 and PO325.

Next is to rule out the basics.

Make sure there aren't any air leaks.

Use a noid light to confirm all the injectors are firing.

Use an in-line spark tester to confirm spark is reaching all the plugs.

Use an engine vacuum pressure tester to rule out any engine vacuum leaks.

Use an engine vacuum pressure tester or exhaust back pressure tester to rule out an excessive exhaust back pressure issue.

Post the results of a compression and cylinder leak down test.

Post the results of a fuel pressure and volume test that was done with a fuel pressure gauge.

You stated you changed the fuel pressure regulator, but you’re still losing residual fuel line pressure. Note: that the most likely reason for that is a failing check valve at the fuel pump.
 
  #24  
Old 10-04-10, 09:40 PM
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Originally Posted by cbuddy2005 View Post
Hmmm

I'm thinking a few things here.

just a few thoughts
Thanks for the suggestions.

*I did check the TPS very slow both with the wire harness disconnected (resistance) and with it connected and key on (voltage). Also checked the throttle switch.
*Throttle body has been cleaned twice in the past 6 months, also MAF.
*Cable has decent tension, but I think that would affect the idle more.
*Distributer is pretty clean. There was a little bit of corrosion on the tip of the rotor which I lightly sanded.
*I really don't think the problem is with the ignition system since it is going lean when it has hesitation/stalling. If it was ignition it should show a rich condition. Regardless, wires, plugs, cap, and rotor were all changed 6 months ago.

ASE MASTER

You have a good point there!
I was hesitant to do the rear O2 since it's ~$80 and is not used in engine control. MY understanding of this car's emission control is that the rear 02 will have no impact on the control loop. But I guess I have to do it eventually for emissions....

The knock sensor was replaced around three years ago when the intake manifold gasket was changed. When the car is about to stall, I do hear it knocking so I believe the code is a result of the stalling and therefore can't be resolved until the stalling is resolved.

*Air/vacuum leaks was my next thing but I'm still trying to get my hands on a gauge. I did spray carb cleaner around intake manifold, EGR valve manifold gasket and injector grommets with no detectable change in idle. Also checked air intake baffles, no obvious cracks or leaks.

*I checked noid light 5 months ago when I had the EGR cylinder 4 misfire problem. I will check again to make sure. Still I don't think it's an ignition/spark issue since it runs lean.

*I didn't use an actual spark tester but did use screwdriver/spark-plug test.

*I checked compression 5 months ago, 1-165, 2-165, 3-165, 4-160. I don't have a compressor to do a CLT.

*Fuel pressure is 34-36 at idle. It increases to ~65 when the return is pinched. It can hold the pressure overnight. The pressure does increase ~2-4 psi when the engine is reved. Sorry if I said it wrong but the new regulator IS holding pressure. So I think the check valve is OK. Didn't do volume test yet, need to grab a friend for that.

* Don't have a exhaust back pressure tester, but the fact that it runs fine in limp mode should rule out a bad cat. Also at higher speeds (45+ MPH)and RPMs the problem is non existent. It's just difficult to get up to speed.

So I think my main focus will be on vacuum and air leaks. Need to get my hands on a vacuum gauge. Oh yeah, and replace the rear O2S.

Thanks, i appreciate the time you both spent responding.

P.S. I ordered a USB PC scanner from Amozon "ElmScan 5 Compact USB (423001)" for $38 shipped. I hope to learn more about fuel trims, O2 sensors, mass air flow rate, temps. It won't necessarily help me with this car but it is a fun tool and good for first look diagnostics.
 

Last edited by EZRydr; 10-04-10 at 09:52 PM. Reason: Updated comments.
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