High Idle Solution - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 9 (permalink) Old 03-20-2011, 07:14 AM Thread Starter
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High Idle Solution

ok new to the forums so i will give a brief history here. i am a race car mechanic. i work on audi, bmw, mercedes, porshe, ferrari, and about a dozen open wheeled race cars. i can fix just about anything i come in contact with on cars worth upwards of 150,000 dollars. i drive a 2006 cobalt ls worth about 13 grand brand new. it now has 130,000 miles on it and really has never gave me an issue what so ever.

so now the problem. i get a check engine light. don't remember the specific fault number but it was for the MAP sensor. i see that it is behind the throttle body so i decide to pull it out just to make sure it wasn't plugged up with some carbon or something stupid before i go on replacing it. (stupid thing is 55 bucks at my wholesale cost) since i took the throttle body off it was fairly dirty i had never cleaned it in 130k miles (it wasn't real bad i do only run 89 octane shell gas in my car) but none the less dirty. so i clean it put everything back together order a map sensor and start my car up and it rev's to 2 grand and stays there. so i think vacuum leak. i check everything no luck. and i know that our cobalts have a strange little adaption memory for how you like to drive and what not and that probably needs reset to correct the throttle. so i clear the faults out of it no luck. i disconnect the battery for an hour. no luck. now i leave work angry and drive home with this car revving stupid high at idle. i take it home convinced there has to be a vacuum leak. took everything back off decide that the stupid intake manifold is probably cracked so i take it off for a full inspection. ( i know decide to clean my intake runners in my head as they were also dirty) found no cracks nothing wrong. then i found a throttle calibration procedure on the net about letting the key on for like 30 seconds and it goes through the motions. which it did i watched the throttle blade move around then go back to the rest position. started it and it still rev's to 2 grand. so battery got unhooked again when i hooked it back up i turned the key on for 30 seconds again then slowly pressed the gas pedal in to wot and held it there and then slowly backed off of it. it was a long shot but i thought that may set the range in it. also did not work. so everything i am finding at this point is to have the ecm reflashed. which sounded crazy. but everyone is saying they had to do that nothing else worked. then i found someone said they slipped the clutch in 1st gear to drag the idle down where it was supposed to be for 1 minute and it fixed it. also that makes no sense what so ever the the ecm is thinking the idle should be a 2 grand then it should be fighting this little action all the way. but i try it anyways and IT WORKED. at midnight last night down in my garage my idle finally is resting at like 750 to 800. sorry for the crazy long post but no one has any idea just how pissed off i was at this. i justed worked on a supercharged v8 jaguar at work that day and fixed it and i was getting my @$$ handed to me by a f'n cobalt.
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post #2 of 9 (permalink) Old 03-20-2011, 07:54 AM
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Had the same thing happen to me last month, was headed to a dr appt on monday (400 miles away) so I decided to clean the throttle body the sat before and did the same thing. spent all weekend on the net trying to fix it with all the remedys but to no avail. took it to the dealer monday morning before my trip and had the ecm reflashed. Really wished id read the threads about unplugging the battery before cleaning..LOL

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post #3 of 9 (permalink) Old 03-20-2011, 08:25 AM Thread Starter
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oh i didn't read that. so if you just unhooked the battery before you start anything it will be ok? i don't see that working either since unhooking it afterwards doesn't do a damn thing. and an update last night after i got it to settle down a drove about 10 miles. it stayed settled down. just took a ride this mourning. it is back up. i was able to settle it back down again but i am going to try a learn procedure i found after it is settled down. i guess let it run for 3 minutes off for 1 minute repeat 3 times. hopefully that fully solves my problem. the real kick here is i have diagnostic tools for every foreign car out there but i can't read any data for a domestic car. if i could really see whats going on in that ecu i might be able to better go about this.
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post #4 of 9 (permalink) Old 03-20-2011, 09:50 AM
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From what Ive read having the battery hooked up while moving the butterfly will relearn the idle position. there are many posts(that i found afterwards) that say unplugging the battery beforhand will stop this from happening. I tried a bunch of remedies that i found online and none of them worked. only after i paid the stealership a hundred bucks to reflash the ecm did it idle normally.

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post #5 of 9 (permalink) Old 03-20-2011, 10:52 AM Thread Starter
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ya but i had the throttle body off the car and unplugged while cleaning it so the battery disconnect is bs since the damn thing wasn't even plugged in while i was moving it. another update i just drove like 30 miles when i came back idle was back up to 2 grand. i shut it off and settled it back down didnt take much to do it but i am now going to let it idle at its normal 750 800 rpm range for like 2 hours afterwards i may light the car on fire. this is driving me insane how can i rebuild a porsche engine and not be able to fix my own f'n cobalt!
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post #6 of 9 (permalink) Old 03-20-2011, 11:16 AM
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hey i feel for ya! i was so pissed i fcked mine up before leaving for an important trip by something so simple. just lettin ya know my experience. i actually took it to two dealers. the first one told me that everything was fine computerwise and that it was probably a vacuum problem. i told them to reflash it anyways but they basically refused. they hooked it up to the comp and said everything was talking to each other and the problem was not electronic. they said theres no way that moving the butterfly would screw up the idle. also mine would start at a normal idle it would only idle high once i touched the throttle. so i took it to another dealer and didn't tell them what was wrong, that i just wanted them to reflash the ecm. they said no problem and viola! all better.

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post #7 of 9 (permalink) Old 03-20-2011, 01:26 PM Thread Starter
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well i may have to go that route..........i might kill some gm engineer if i do. but after getting it settled down again i let the thing idle for like 2 hours. its stayed good right around 750 then i went for a drive to the store shut the car off came out a half hour later and it was still good. its been off for about 2 hours and i just started it up and its still good. but i will know for sure after i get to work tomorrow which is about a 30 mile drive if its ok. this is madness. out of all the new technology i work on this makes me want to dump a 350 small block in it with a 4 barrel holley and give me a rear wheel drive cobalt with 1970's technology
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post #8 of 9 (permalink) Old 03-21-2011, 09:15 AM
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Just cleaned the throttle body on the wife's car(2005 Cobalt 5spd) had the same issues with the high idle that I have read it seems a dozen times. I was to the point of taking it somewhere and letting someone reflash her computer. But a CEL never came on. So the engine thinks it is running normal. I never thought to manually make the car idle low by slipping the clutch in first gear like i read in fastcompany's post. I went to go do that and it just seemed like that was a little hard on the clutch so I idled around the neighborhood in first gear riding the brakes(brakes are a little easier to repalce than a clutch) and I cant believe that fixed it!(for now) I am kinda feeling like fastcompany, I want to choke slam some gm engineer!! Thanks fastcompany!
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post #9 of 9 (permalink) Old 03-22-2011, 04:01 AM Thread Starter
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hey just an update that worked for me for like the first couple test drives then it shot back up. it wasn't until yesterday on my drive to work where i had calmed it down 3 times on the way there but on the way home it was good to go. and i tried riding the brake around in gear but every time i would go about it a car would get behind me....
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