my bucking car

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  #1  
Old 12-08-07, 08:54 PM
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my bucking car

been trying to figure this one out for a while now..
acura rsx-s, manual tranny.

when car is in gear, and im NOT shifting or on the clutch, but simply modulating the gas, the car bucks with each step on the gas and each release of the pedal.

its most prominent in 1st and 2nd gears when coasting in traffic, and letting foot on and off gas to maintain speed. you can see the tach bounce in sync with the car bucking, typically around 3-400rpm.

it tends not to do it if im over 5k rpm. (open loop)

im not stepping hard on the gas, but simply gently letting on and off. as a matter of a fact, when i mash the gas pedal, the buck isnt prominent.. but thats not too practical in traffic.

no clue what it is. electrically related? tranny? checked the engine mounts, they are solid.
 
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  #2  
Old 12-08-07, 09:56 PM
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I assuming a couple of things. The rpm range it occurs is 3k-4k and the throttle linkage and throttle body doesn't have a hitch it, which you would notice right away with the engine off.

As far as the engine doing it, I would say MAF sensor. But if it acts like something with play in it, I would lean toward CV joints or possibly clutch spline.

Did it start doing it suddenly or did it start a little at a time and get progressively worse?

Bob
 
  #3  
Old 12-09-07, 02:48 AM
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Perhaps TPS? Throttle position sensor. I believe you can test those with an ohmeter. Remove connector, and touch meter probes on pins of potentiometer (TP sensor). Not sure which 2 in your case but trial & error should work. Ohmeter should move (analog) or number should increase gradually & smoothly, as accelerator pressed slowly. If it doesn't move slowly, but suddenly jumps, it's defective. Tried this a while back on a Dodge & it proved/confirmed, that I had a faulty throttle position sensor. Symptoms were similar to yours.
 
  #4  
Old 12-09-07, 04:34 AM
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Originally Posted by marbobj View Post
I assuming a couple of things. The rpm range it occurs is 3k-4k and the throttle linkage and throttle body doesn't have a hitch it, which you would notice right away with the engine off.

As far as the engine doing it, I would say MAF sensor. But if it acts like something with play in it, I would lean toward CV joints or possibly clutch spline.

Did it start doing it suddenly or did it start a little at a time and get progressively worse?

Bob
its been like this, no better or worse, for a while now.

almost feels like pedalling on an excercise bike, then speeding up fast enough to get the belt freely spinning, then trying to pedal slower and catch the belt, theres that type of free play feeling present.

no MAF on this car. clutch is brand new, so im assuming the components were all checked during replacement.

cv joint makes sense, its that sort of feeling. ill jack it up and check, but they dont exhibit any other signs of problems. no clicks, launches fine, etc.

maybe a bad ground? i hate just guessing at stuff because its makes it too hard to find the problem :/
 
  #5  
Old 12-09-07, 06:37 AM
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Back to Mike and the TPS. That sounds like a good possibility. It's hard to tell from a distance if it's free play or engine electrical.

If there's no MAF sensor, there should be an equivalent. What year Acura do you have?

If it was a ground outside the sensors that work in conjunction with rpm/throttle position it shouldn't show up at specific rpms. I'm understanding that full throttle doesn't have the problem. This all points to Mike's thinking it's TPS or the equivalent in that vehicle.

If there are codes to guide you it takes a lot of the guessing out of it, but outside the codes there is still a lot of things to deal with. Sometimes (and I hate to say it) you have to wait until it gets worse to figure out what it is.
 

Last edited by marbobj; 12-09-07 at 06:58 AM.
  #6  
Old 12-09-07, 08:39 AM
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Originally Posted by Mike.B View Post
Perhaps TPS? Throttle position sensor. I believe you can test those with an ohmeter. Remove connector, and touch meter probes on pins of potentiometer (TP sensor). Not sure which 2 in your case but trial & error should work. Ohmeter should move (analog) or number should increase gradually & smoothly, as accelerator pressed slowly. If it doesn't move slowly, but suddenly jumps, it's defective. Tried this a while back on a Dodge & it proved/confirmed, that I had a faulty throttle position sensor. Symptoms were similar to yours.
assumed the tps a while ago, but dismissed it since idle is rock solid. ill have to measure resistance and voltage. maybe ill be lucky and this is it..
 
  #7  
Old 12-09-07, 10:01 AM
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Originally Posted by marbobj View Post
Back to Mike and the TPS. That sounds like a good possibility. It's hard to tell from a distance if it's free play or engine electrical.

If there's no MAF sensor, there should be an equivalent. What year Acura do you have?

If it was a ground outside the sensors that work in conjunction with rpm/throttle position it shouldn't show up at specific rpms. I'm understanding that full throttle doesn't have the problem. This all points to Mike's thinking it's TPS or the equivalent in that vehicle.

If there are codes to guide you it takes a lot of the guessing out of it, but outside the codes there is still a lot of things to deal with. Sometimes (and I hate to say it) you have to wait until it gets worse to figure out what it is.

no codes, and tired of having to wait this thing out and see if it fails

TPS resistance measured good across all points. doesnt mean its ruled out though.

its a 2002.

im leaning toward mechanical prob since thats what it most feels like. maybe the timing chain tensioner is failing?
 
  #8  
Old 12-09-07, 12:48 PM
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When cruising and you push in the clutch, does it coast good or try to slow too quickly?, as if you have a drag you did not used to have?

Is this bucking the same amount even if you get in car, and get going quickly without warming it up much, and test this out just down the road as soon as you can, where you have not either heated the engine, brake parts or wheel bearings? And compare how the bucking is then, compared to a longer run with the engine and car parts all heated up? [Just throwing some easy tests out there that may not have anything to do with problem, but because these can be tested so easily...]

And you should also be able to test your loose timing theory easy enough somehow by rotating engine back and forth by hand in neutral to see if valvetrain/distributor? linkup is tight and moves right away when the crank is moved. Are you able to make such a determination without having to take off many car parts? On a car like mine, I can pull on say an alternator belt and remove timing cover peep hole to see if big cam gear rotates right away, for example, if I wanted to (or the distributor that is right out front and accessible). And do this back and forth, which is a must since if you did the test just one way, the belt may have been taut at that moment.

And this is something I have never done with a frontdrive car and maybe someone else would have this answer, - but what if you jacked the front wheels off the ground and tried to turn them when in gear and feel how long it takes in trying to rotate tires, before the engine stops you. THAT too may be interesting. Should there be quite a positive tight lockup, or is there naturally quite a bit of play, even in new cars, when doing this? The reason I bring this up is the fact the poster is on and off the gas which would replicate the throwing the load back and forth between the transaxle and engine, and if the lockup is not tight, you'd naturally feel that by getting on and off the gas while in a manual trans car.
 
  #9  
Old 12-09-07, 01:49 PM
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sounds like a classic egr port issue. try disconnecting the egr vacuum line to see if it goes away
 
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