'94 Ciera 3.1L V6 engine idle/running issues

Hello! I've been searching and searching for things, and i've been reading through a Chilton's book I have for that car and I'm at a loss as to what this is. Basically, it appears to jerk or stutter while running and only occaisonally. Say I am on a highway going 65mph and let up on the gas to maintain that speed (I inherited a car without cruise control--fine with me)...most of the time it will eventually seem to jerk or stutter and it won't stop until I accelerate or let go of the pedal.

The feeling is as if you're going over a lot of rocks, only you can feel it in the driver's seat and nobody else seems to. It seems as if I can feel it on the accelerator pedal itself. It only happens occaisonally, and it ALWAYS goes away if I accelerate (even if only a little bit more). I don't see a check engine light or anything when this happens. The car has ~115k miles on it, and around 100,000 it had a rebuilt transmission installed into it because the clutches burned out. We could be classified as experts, but we had someone else install that. You don't have to dumb down any advice :).

The car ALWAYS starts up fine, and it seems to be idling better than ever now. We recently replaced the radiator and the engine coolant temp sensor and it also received new tires (Goodyear Regatta 2...fantastic choice as well). Someone else in this house said a co-worker told him of a similar problem and replacing the MAF sensor fixed it. Does this sound like the problem is the MAF sensor?

It also has another minor problem. When I put it in park and I'm about to turn it off, I noticed that it is as if the engine is revving itself up. It literally sounds like its doing that, and sometimes you can feel the dashboard shake right before it appears to rev itself up. The LED clock and headlights appear to dim for a second after the sound that seems to mimic punching it down a bit. If you punch the accelerator, it goes away, but it also eventually goes back to a normal idle if you just let it do it. I was thinking of maybe putting some fuel injector cleaner in it, but does anyone know what that problem might be?

Keep in mind that these NEVER happened before until only recently (~6 months), and they are absolutely consistent as well. It is starting to use up a LOT of gasoline now too, so i'm getting a bit desperate here. Thanks for ANY help you guys can be of. I was searching google for something like this, and automotive forums came up first. :)

With mileage being what it is I would say you might want to check coil packs. I had one go out about 120,000 and another at about 121,000. While your problem doesn't sound exactly like mine it is quite similar. As far as the bad gas mileage goes, you might want to check O2 sensor(s).

With mileage being what it is I would say you might want to check coil packs. I had one go out about 120,000 and another at about 121,000. While your problem doesn't sound exactly like mine it is quite similar. As far as the bad gas mileage goes, you might want to check O2 sensor(s).

Well I did solve the bad gas mileage by replacing the PCV valve. I knew it wasn't the O2 sensor because that sensor by itself is quite new.

I haven't considered the coilpacks, do you have a general idea of how much that might cost? I'll go check sometime later today.

Mine were replaced at the dealer and I think they charged around $200 each time

Mine were replaced at the dealer and I think they charged around $200 each time

Wow. Well I do everything myself, and it looks like I can get the part for around $51 actually. I made sure I had the right one, because a relative of mine has replaced it on a 92 cutlass before.

Replace your tps sensor. Make sure your IAC is learned.

Replace your tps sensor. Make sure your IAC is learned.

Excellent advice, I never thought of that one. I will test the coil and see if it is bad, and then I will check out the throttle position sensor next. How's that sound? Its just that since we have also had the coil replaced on another cutlass, I'm leaning towards that first. However, I was told the problem it fixed with that one was that it would kill while idling after driving it. Not quite my problem, but i'll go in that order anyways.

I never thought about the IAC/TPS idea, but that makes sense to me.

I am having exactly the same problem. Did you ever find out what was it? IAC/TPS or coils?

Excellent advice, I never thought of that one. I will test the coil and see if it is bad, and then I will check out the throttle position sensor next. How's that sound? Its just that since we have also had the coil replaced on another cutlass, I'm leaning towards that first. However, I was told the problem it fixed with that one was that it would kill while idling after driving it. Not quite my problem, but i'll go in that order anyways.

I never thought about the IAC/TPS idea, but that makes sense to me.

I am having exactly the same problem. Did you ever find out what was it? IAC/TPS or coils?

I haven't checked the IAC/TPS yet. I am holding off on the surging issue for that one. My engine idle and misfiring problems when trying to maintain a speed did get fixed though. You know what they were? The spark plug wires were ARCING and I had two plugged fuel injectors. We had absolutely no time to test things anymore so we took it to a goodyear repair shop nearby (one of those franchises) that we go to for small things and tires. They cleaned the fuel injectors and we replaced the plug wires ourselves. The total cost wasn't even $200 ;).

After that, it idles PERFECTLY at stop lights and no longer misfires. Also, it seems to launch forward with much greater power. Its probably a combination of the double-platinum plugs, better plugwires and clean injectors.

On a side note, the coils were all perfectly fine. Occaisonally, the idle is only mildly rough at idle in a park position and not all the time. I suspect that this could be tied to the surging when the car is in park, and I am suspecting the TPS moreso than the IAC. My research findings point more to the TPS than the IAC, if that helps you.