About 2 weeks ago after cruising on the expressway at about 75 mph for 20 miles or so, I came to a stop at the end of an exit ramp, and my Cobalt idled "rough" for about 10 seconds. It bounced between about 500 and 1000 rpms until it settled in at 800. I thought it was an isolated incident until it happened again just yesterday. So far, it has thrown no codes and it runs perfectly otherwise.

My question is this: has anyone else had this happen to them? Its got about 1800 miles on it now, and I'm getting ready to mod the car (now that I've had it for a whole month ), and I want to make sure everthing is in good working order before doing anything.

Thanks,
Chris
'06 G85 Cobalt SS

 

I bet you had your A/C on. Mine did the same thing but only with the A/C running, while I was sitting at idle after coming to a stop(did it all the time). Maybe something to do with the drag from the blower and the A/C unit. Other than that, I have no clue.

All I can say is that I think it's a normal operation of our strange cars.
These things are finicky.

 

Mine does that all the time, even when I dont have the AC on. Every time I drive the idle stumbles alot when im at a stop.

 

Mine does it too, I don't think its anything to worry about.

 

Mine does it also. After long drives it will stumble a little. I am also getting a p0171 CEL. I do not know if it is related or not???? The dealer is going to install a new air filter GM part number 15239447.I am not sure if it will help ether case but I will see.

 

Mine does the same.... who knows.

 

Mine stumbles after I back out of the driveway. The tach dips to below 500 RPM 3 times and then returns to normal. Every now and then I get a loss of power sensation when I am accelerating away from home or the office. It is probably the same thing occuring. I would like to know what it is, but it is impossible to diagnose as it happens irratically.

 

Must be a problem with everyones cars. Mine does it also but Im not worried about it since my trans am did it everynow and then too for whatever reason.

 

Well, that's a bit of a relief. I was hoping that I wasn't the only one ... now, who'll be the first to figure it out? The problem for me has been the same as many of you have already mentioned - it's not predictable or easily repeatable. It's happened to me since my original post without the A/C on as I was pulling into my garage. What gives?

 

Replacement of your filter may fix your problem, the original filters folds may be too bunched-up. Advise the Dealer to not only clear the DTC, but also reset the fuel trims. I have done this with succes and no repeated failers. As for the idle, there is an update for the PCM to address idle quality issuses. My own SS/sc had the same problem and the reprogramming elimminated the concern.

 

Has anyone else taken theirs in for this? I noticed it yesterday after getting off of the freeway (only doing about 75 the whole way) and at the traffic light it started jumping around between 500 and 1200 RPMs for at least 10 seconds before I eventualy just gave it a bit of gas for a second and it went back to normal. It hasn't done it since then, but I have seen it jump around before, but not as much as the 500 and 1200. I almost thought it was going to stall out.

I can also guarantee that in Washington right now, I didn't have the A\C on

 

My Car has been doing the same thing. Wierd guys I am at school do you think its possible to take the car to another Chevy dealer, because the place I bought the car is about 4 hours away?

 

You can take it to any chevy dealer, possibly any gm dealer(not sure about that though). I had a problem with my 03 F-150 that stumped the techs at the dealership where I purchased it, so I took it to another Ford dealership and they fixed it in 20 minutes - needless to say, I wont take it back to the dealership that I purchased it from.

 

Mine does the same thing but only when I first start it up. It'll fluctuate from 300rpm to about 900rpm then back to 300 like 4 or 5 times. I also get the lack of power when first pulling out like Spite4U said, just casually pulling out of my driveway in first the car like rocks as if it's not getting enough fuel. I took mine to my dealer for the idle fluctuation and they couldn't duplicate, never looked into it further. This is also with the A/C off

 

My SS/SC does it also but very rarely...only after I've been pushing the car or after long drives over 60 mph. However, I didn't realize that this is also happening to 2.2L Coblts as well. This must be a normal occurence that may have to do with how the PCM is calibrated and it could be the computer trying to get the A/F mixture back to proper levels or the computer is making adjustments for safethy reason.

 

I just bought my car yesterday But I did notice this as well, when you put it in nuetral or come to a stop sometimes (I saw it about 3 times yesterday) for a few seconds the idle will jump up and down from normail to about 1100 and then settle back down and everything is fine. A friend of mine said hes seen it before in other cars and said its normal.

I dont think its anything to worry about. I wouldnt waste your time trying to get the dealership to fix something that you already know they cant.

 

Apparently there IS a PCM update to resolve this, mentioned in another thread.

https://www.cobaltss.net/forums//showthread.php?t=5908