Idle Issue - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

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post #1 of 36 (permalink) Old 02-28-2011, 11:50 AM Thread Starter
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Idle Issue

here is my problem:

anytime i have to come to a stop my idle drops to around 500 rpm. it almost seems like the car is going to stall, but then it picks back up to about 750-800 rpm. i notice this a lot when i stop after reversing. once i put the car into drive, it picks up.

anyone have an idea on what this could be. thanks for the help in advance!!
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post #2 of 36 (permalink) Old 02-28-2011, 04:52 PM
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sometimes as i idle, or coast, my rpms like to bounce up and down.
im not sure what the cause of this is, but instead of me opening a new topic, ill just post on yours, hopefully someone has an answer for both of us
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post #3 of 36 (permalink) Old 03-03-2011, 10:21 AM
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Had this problem with mine (except a little worse...she'd actually stall out). It's currently in the shop getting the final fix. :-) What kinds of codes (if any) is yours throwing? If they're related to throttle position at all, try cleaning out your throttle body (they sell stuff to do it at Autozone). If that doesn't help, hit up Autozone again and get some Mass Air Flow sensor cleaner and clean your MAF sensor. If THAT doesn't help, I'm guessing that you'll probably need to either A) replace the throttle body, B) replace the coil pack, or C) replace the ECM, depending on what kinds of codes are being thrown.

My hubby cleaned out and later replaced my throttle body (she was throwing the throttle position codes), cleaned my MAF sensor (still stalling after new throttle body), replaced my fuel filter (VERY early on when this problem first started...hubby thought it was just bad gas), AND replaced all 4 spark plugs (threw misfire codes on 2 & 4) trying to get this issue figured out. My mechanic was leaning towards it needing a new ECM, but the latest code thrown on her (intermittent misfires) pointing towards the coil pack. I lucked out and he had a used one that he was able to test it with and sure enough, she's no longer missing. He's cleaning the fuel injectors as I type and is going to drive her around a bit to make sure, but he's 99.9% sure she's good to go. Had the new code that she threw been related to the throttle body, he would've had to replace the ECM. Apparently, my throttle body and coil pack both took a crap at the same time. My hubby was able to fix the one, but was getting tired of just trying "pipe dreams", as he put it, so we caved and took her in.

Also, IF you have an 06, check out the service bulletin and recall section on here. There was a recall on the fuel injectors back in 2007 (I think) that might apply to you and could possibly be the cause of all this.
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post #4 of 36 (permalink) Old 03-04-2011, 07:08 AM
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i'm having idle problems too. it bogs down to 4 or 500 and bounces for a few seconds before smoothing out, i had an emissions code but it's since been fixed, i tried cleaning the MAF, it shakes like a jackhammer when coming to a stop, headlights dim, ac or heat dies down a bit and its really annoying, my CAI rattles off the front cross piece when this happens and it's really loud.

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post #5 of 36 (permalink) Old 03-04-2011, 07:36 AM
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that damned Ethanol will destroy non flex fuel cars. I almost had my wife's grand am die on her because of the crap clogging up the cat converter. And i'm sure that the stuff isn't doing any good for the injectors and spark plugs either.

My grandfather told me that back when moonshine was being run, gas also had lead in it, and the lead contradicted the bad effects of the ethanol that some people dumped in their tanks when running low.
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post #6 of 36 (permalink) Old 03-04-2011, 08:50 AM
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I know it sounds a little too simple, but ii had this problem in an old pontiac i used to own, and it turned out to be a vacuum line popped off. have you checked that?
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post #7 of 36 (permalink) Old 03-04-2011, 10:17 AM
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If it's not a vaccuum issue, buy a nine dollar can of Seafoam, follow the directions on the can, problem solved.
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post #8 of 36 (permalink) Old 03-04-2011, 03:58 PM
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G5Steven - you are making me feel real old, I remember in high school and after 1983-1985 that most gas had lead in it, that is why today it says unleaded. Back in the 80's there was no such thing an unleaded.
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post #9 of 36 (permalink) Old 03-04-2011, 08:22 PM
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Vacuum leak, clogged/dirty air filter, 02 sensor, faulty MAF, clogged cat, injectors etc.. There's many possible cause's for this issue. Time to start the process of elimination.

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post #10 of 36 (permalink) Old 03-05-2011, 05:12 AM Thread Starter
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yeah, i think i will start by seafoaming it. ill also get some MAF cleaner and try that.
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