every time i start it, the egine starts, revs up to 1500 then back down to maybe 600, then back up to 1500. it sits there and does this for about 10-15 seconds. anybody know what the damn problem is?

 

my does that every once in away, its a TB wirin problem i think, for my if i shift it bac to neutral after i put it in gear it fixes itself

 

Changed anything relating to any vacuum lines? I know when some people have a small vacuum leak (like i did) the engine will rev and plummet as it tries to correct the vacuum leak. Take a look around your intake mani and see if all the hoses are connected. I doubt it'd be the brake booster since it's a huge vacuum line but it runs from the back of the intake mani on the drivers side back toward the driverside firewall. That's all I got though, good luck.

and why not take it down to a dealership and have it fixed under warranty?

 

well my bumper-2-bumper expired at 30,000. since then i have modified my intake, my exhaust, my suspension, and my interior. So if i tried to take it to the dealership, they would probably laugh and slam the door in my face. I havent tampered with the intake mani. The guy who had the car before me must have really beat it up. Within 3 months, the clutch went out. It was ridiculous that the dealership wouldnt even cover under warranty since its considered a "wear and tear" item. The jerk that runs the service department accused me of being an inexperienced teenage driver...even though i learned how to drive with a clutch.

 

That sucks bro! I hope that Maven chimes in on this, he's definitely one of the MOST KNOWLEDGEABLE guys on here about the cobalt, if anyone can help from afar I'd say it is definitely him.

 

sounds like a messed up TB blade or a vac leak somewhere.

does it happen when you have AC on or all the time.

 

Check vac. line and try cleaning the throttle body, if all else fail, dealership? : /

 

clean the TB..........youd be suprised at how much crap builds up there and they could be your proble with the idle.......do you have a 2.4 manifold?

 

i agree, clean the throttle body and it will solve your problem, cobalts are known for this, make sure you connect all your sensors back up or you will think ur engine is blown up ahah

 

i clean the throttle body every oil change. lol.

 

it also does it on cold starts, like the first time u start the car for the day or its been a few hours, just idles a lil rough