IAC valve
 

Where is the IAC valve loacted on a 1999 silverado with a 5.3? I think mine is going south and I was wondering if it is easy/cheap to replace or check. Does anyone have any expierence with one? Thanks!!!
Rob

RE: IAC valve
 

What symptoms do you have that make you think your IAC is going south? It seems to me that one of the simplest tests to verify that the IAC is working is tolook at the idle speed, then turn on various accessories such as the A/C, etc. and verify that the idle speed is maintained. Putting the vehicle in gear and verifying that idle speed is maintained should be the final test I would think.

This link isn't particular to your vehicle, and probably isn't a thorough way of testing, but definitely can help get you started in the right direction.
Testing IAC valve on 1988-98 Silverado

Do you have the Factory Service Manual? I'd imagine it would go over the testing or diagnosis in aspecific manner. Of course, if they tell you to use the diagnostic scan tool, then it's not too much help.