Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Which engine does it have, and have you checked it for vacuum leaks.
The best way to check for vacuum leaks is to get a can of WD40 and spray all around the intake manifold, and vacuum lines. If you hit a vacuum leak it will speed up for a second or two. That allows you to find almost impossible to locate vacuum leaks. If that doesnt solve the problem, I would suspect the IAC. It controls the idle speed via the ECM. Think of it as a robotically controlled idle speed system. The IAC might be bad, it is a fairly common failure. There is a reset procedure for the IAC. You remove the ECM fuse for a few minutes, reinstall it and fire up the engine, immediately placing it in gear with your foot firmly on the brake. This makes the computer re calibrate the idle speed. Sometimes it takes a few tries. If it has a vacuum leak, or the IAC is bad it wont re calibrate. One last thing is if you have a vacuum leak the IAC cant do it's job, that makes it critical to search for vacuum leaks first.
Okay, let me know if you have any more questions, I will be happy to help.