So ever since I bought my L98 GTA two years ago I thought that it idled a bit ruff when it was in gear. It doesn't idle erratically, or seem like its going to stall or anything, the engine just shakes the car more than I would like it to when its in gear. The car only has 86K on it, and is all stock. When warm and stopped gear it idles at about 350rpms. In neutral it stays at about 500 rpms. I replaced the Idle air control valve with a brand new one 2 weeks ago to see if this would help the problem. When I did this I took off the throttle body and sprayed it down with carb cleaner. The first IAC valve I had kept the idle at around 500RPM in gear, and the car ran smooth as silk. I LOVED the way it ran. That IAC valve took a dump the next day and would not stay adjusted right. It kept stalling out the car, so I went and got another one. This IAC keeps the idle the same as before I changed anything, a little ruff. I made a thread on the GTA source page and they I heard that the idle speed in gear is supposed to be around 475-550RPMS which was where the engine idled beautifully with the IAC that took a dump a day later. So I ask How do I increase the idle speed about 100 or so RPMs during idle? Should I attempt doing this? thanks!

 

This is a way to manually set the idle.
http://www.corvetteforum.com/techtip...D=55&TopicID=2