I have a 1985 Corvette that has 170 thousand miles on it. Its just now starting to give me some problems. But the one im concerned about the most, is my idling. It jumps around now during idle in park and drive. Sometimes it'll idle at 850 in park, and all of the sudden it'll jump to 1300 and sometimes 1500. And it will stay there for a good amount of time. Then out of no where, the idle will come back down. Its been doing this for a few months now. Recently it got so bad that it was sounding like I had a missfire. So after some long reading, I came to the conclusion that my IAC valve (idle air control) was taking a crap. I replaced it and the "missfire" went away. But im still having my idle jump around on me. Can you guys give me an idea of what this problem might be.