High Idle
#1
10-02-08, 04:49 PM
High Idle
I have a 1989 Ford E250 straight 6 cyl. The engine is racing at a very high speed. I changed the air idle speed valve but it did nothing. The throttle plates seem to be closing all the way. I can't find any vacuum leaks except that there are two hoses on either side of the air idle speed valve the go into one and it's just hanging on the passenger side of the manifold. I can't find a port that is missing a hose. The hose isn't sucking any air at all, which is strange. I'm at total loss as to what could be causing the engine to race. When I put it in gear, it runs rough.
#2
10-03-08, 05:44 AM
The hose you have hanging is probably going to a port that is sucking air. What you have is a typical vacuum leak.
Here is vacuum diagram link for your truck:
http://www.autozone.com/shopping/rep...00c152801cd6b6
With your throttle plates closing properly, I'm sure when you get the vacuum leaks sealed off the engine idle will drop.
Here is vacuum diagram link for your truck:
http://www.autozone.com/shopping/rep...00c152801cd6b6
With your throttle plates closing properly, I'm sure when you get the vacuum leaks sealed off the engine idle will drop.
#3
10-03-08, 07:20 AM
I found out where the hose goes. It goes to a second port where the PVC valve is but it didn't solve the problem.
If I cover the 2 big ports where the throttle plates are, shouldn't the engine stall or at least show some change in the idle?
I can't find a crack in the manifold. How else could the air enter to maintain such a high idle. The engine is spinning as if I were going 35 MPH.
If I cover the 2 big ports where the throttle plates are, shouldn't the engine stall or at least show some change in the idle?
I can't find a crack in the manifold. How else could the air enter to maintain such a high idle. The engine is spinning as if I were going 35 MPH.
#4
10-03-08, 08:50 AM
If you have a power brake booster = vacuum powered, that would be a source. An inline 6 really doesn't have too many possibilities for designed vacuum ports. If you have an automatic tranny, there is probably a vacuum modulator on the transmission (I doubt if that one would be computer controlled).
You may be able to find it by spraying WD 40 around the intake mating surface to pinpoint a gasket leak.
The PCV line would be another possibility. Many of the port-hose connections can leak, but it would to be a big one to cause that type of idle step.
I would take a few minutes, with a can of WD40 and work your way around the hoses and there connections. Spray a little of the WD 40 on them and see it that makes any difference in the idle. If you have a timing light, check the timing on it to make sure something hasn't stuck in the distributor advance. If nothing there, pull off the brake booster line (if you have one) and plug the end of it to check leakage at the booster.
For a vacuum leak, if you plug any of the known vacuum sources with throughput = PCV line, the idle should drop. If it doesn't, it could be ignition timing. = distributor advance or timing chain.
As far as the ports at the throttle plate, many of those are regulated ports = no vacuum until the throttle is opened. A regulated port wouldn't affect the idle.
You may be able to find it by spraying WD 40 around the intake mating surface to pinpoint a gasket leak.
The PCV line would be another possibility. Many of the port-hose connections can leak, but it would to be a big one to cause that type of idle step.
I would take a few minutes, with a can of WD40 and work your way around the hoses and there connections. Spray a little of the WD 40 on them and see it that makes any difference in the idle. If you have a timing light, check the timing on it to make sure something hasn't stuck in the distributor advance. If nothing there, pull off the brake booster line (if you have one) and plug the end of it to check leakage at the booster.
For a vacuum leak, if you plug any of the known vacuum sources with throughput = PCV line, the idle should drop. If it doesn't, it could be ignition timing. = distributor advance or timing chain.
As far as the ports at the throttle plate, many of those are regulated ports = no vacuum until the throttle is opened. A regulated port wouldn't affect the idle.
#5
10-03-08, 10:06 AM
I checked all the hoses, the power booster and sprayed everywhere. The ports where the throttle plates are have vacuum and I was told that it should stall if I block them. You're saying that it wouldn't be affected. If that's the case, could the Throttle Pressure Sensor be the problem?
As far as the timing chain goes, could it have jumped a tooth?
As far as the timing chain goes, could it have jumped a tooth?
#6
10-03-08, 10:53 AM
The ports at throttle plates come in two types - regulated and unregulated. If yours have vacuum with the throttle plates closed, they are unregulated = have vacuum all the time. If that is the case, then the engine should stall out since the vacuum at those ports are involved in a certain fuel/air mixture. By blocking them the fuel air mixture would suddenly get richer and the engine would stall because of it.
However, looking at the big picture.... If the engine is not stalling after depriving it of the air in the vacuum provided by the ports you're talking about, then it has to be getting the air from somewhere = another vacuum source.
Try this, it won't take long to do. Locate all the vacuum lines coming out of the engine. Disconnect them one at a time and hold your finger over the source of the vacuum = vacuum port.
If none of those identify (by dropping the idle) the offending accessory, then you have to assume you either have a vacuum leak at the intake (either gasket or crack) or some of the ignition hardware is at fault. First eliminate the vacuum leak possibilities. Then we'll look at the rest of it.
However, looking at the big picture.... If the engine is not stalling after depriving it of the air in the vacuum provided by the ports you're talking about, then it has to be getting the air from somewhere = another vacuum source.
Try this, it won't take long to do. Locate all the vacuum lines coming out of the engine. Disconnect them one at a time and hold your finger over the source of the vacuum = vacuum port.
If none of those identify (by dropping the idle) the offending accessory, then you have to assume you either have a vacuum leak at the intake (either gasket or crack) or some of the ignition hardware is at fault. First eliminate the vacuum leak possibilities. Then we'll look at the rest of it.
#7
10-03-08, 11:30 AM
Correct, I'm to the point of believing that there is a crack or the intake gasket is bad. The idle is way too high for it to be a 1/4" or 5/16" hose and none of those hoses are changing the idle. It's around 3,000 RPM or more.
#8
10-03-08, 02:16 PM
With this in mind - you have disconnected all hoses and blocked their ports, including PCV line and brake booster line (both of these could effect the idle step you're describing). In having done so you didn't get a change in the rpms. Then the most likely, at this point would be an intake gasket leak/crack. On that engine you should be able to get the WD 40 spray around the intake enough to get an rpm change. Have you done that?
In terms of a timing chain jump, it would have retarded the timing on the valves and ignition, so I would put that at the end of the list.
In terms of a timing chain jump, it would have retarded the timing on the valves and ignition, so I would put that at the end of the list.
#9
10-03-08, 02:38 PM
I'll go through all the hoses again tomorrow but I don't see how such small hoses, even the power booster, are going to keep the car racing at such a high idle (about 3,000 RPM) when I blocked the air at the throttles plates.
A friend of mine was spraying choke cleaner yesterday and I was spraying WD40 today with a second friend. So far we haven't seen any change. I can't get to every place on the manifold near the gasket. It's too crowded.
One more thing: The van has almost 200,000 miles on it. I don't know how much work or money I'm willing to spend on it.
A friend of mine was spraying choke cleaner yesterday and I was spraying WD40 today with a second friend. So far we haven't seen any change. I can't get to every place on the manifold near the gasket. It's too crowded.
One more thing: The van has almost 200,000 miles on it. I don't know how much work or money I'm willing to spend on it.
#10
10-03-08, 05:54 PM
The hoses and their connections are the first thing you have to clear as possibilities, because they are frequently the cause and they can be cleared off the list quickly by anyone. From there you go to the intake, once again because, with a few tricks you can get it out of way.
The only hoses that can effect that size of idle step would be the power booster and the PCV line and either would have to have a substantial leak. If you had a leak of that size in the brake booster, the brakes would show it right off.
The smaller lines, like the vacuum advance (1/8) or some of the emission control jobs can impact the idle speed, but not the increase you have there.
The idle control valve would be next, then the electronic gadgetry that pulls the idle down from fast idle in a cold start. That sensor is the water temp sensor for the computer. If it is reading a cold engine all the time it would have the computer in a cold running condition all the time = fast idle. That is a possibility. Usually when those act up they go the other way and you have cold starting problems.
However, I wouldn't replace electronic gizmos without a fault code. Those things are just too expensive to be guessing at. Outside vacuum leaks, I suspect, the problem is electronic and although you can replace the temp sensor for about thirty five dollars, you may not want to invest the money on a maybe.
You can get a cheap beep reader from an auto parts store for a Ford for about $15.00 or so if you want to go that route. All the stuff starts adding up and with the mileage on the van it gets to be a question mark.
The only hoses that can effect that size of idle step would be the power booster and the PCV line and either would have to have a substantial leak. If you had a leak of that size in the brake booster, the brakes would show it right off.
The smaller lines, like the vacuum advance (1/8) or some of the emission control jobs can impact the idle speed, but not the increase you have there.
The idle control valve would be next, then the electronic gadgetry that pulls the idle down from fast idle in a cold start. That sensor is the water temp sensor for the computer. If it is reading a cold engine all the time it would have the computer in a cold running condition all the time = fast idle. That is a possibility. Usually when those act up they go the other way and you have cold starting problems.
However, I wouldn't replace electronic gizmos without a fault code. Those things are just too expensive to be guessing at. Outside vacuum leaks, I suspect, the problem is electronic and although you can replace the temp sensor for about thirty five dollars, you may not want to invest the money on a maybe.
You can get a cheap beep reader from an auto parts store for a Ford for about $15.00 or so if you want to go that route. All the stuff starts adding up and with the mileage on the van it gets to be a question mark.
#13
10-04-08, 08:31 AM
You found it, huh? At least now you know.
If it was newer or less miles, I would say tear it apart and put in the new gasket. If the gasket failed one place it can easily fail elsewhere. And you really can't put the JB weld everywhere it could fail.
With what you have, though, I guess I would try anything that worked. You wouldn't have to use something with the JB Weld consistency, though. You could try a high temp form-a-gasket.
I think if I was going that route, I would loosen the intake bolts first, then force in the sealant, then re-torque.
If it was newer or less miles, I would say tear it apart and put in the new gasket. If the gasket failed one place it can easily fail elsewhere. And you really can't put the JB weld everywhere it could fail.
With what you have, though, I guess I would try anything that worked. You wouldn't have to use something with the JB Weld consistency, though. You could try a high temp form-a-gasket.
I think if I was going that route, I would loosen the intake bolts first, then force in the sealant, then re-torque.
Last edited by marbobj; 10-04-08 at 08:50 AM.
#14
10-04-08, 08:57 AM
There is a local guy who does work on the side. He might do it for $200 but I think it's time to buy something else. It had a lifter knock until I put 5 quarts of straight 40 weight oil in it. I think $300 is my limit on the job.
#15
10-04-08, 03:47 PM
Yeah, some of this stuff that we've had for a long time and has always worked well for us reaches its end sometime. You may be at that point with the van. With the lifters leaking down and a couple of hundred in the intake gasket, there's other things just around the corner.
#16
10-04-08, 05:16 PM
The JB Weld worked and I bought a 1994 Dodge Ram for $650. You're 100% correct that there are more problems to come with the Ford. I'll use it for a few days until I switch the insurance and register the Dodge.
