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.