Hi I have a 2000 Cavalier z24 with a manual trans. and about 2 months ago it started idling high for a while and for a while it did it most of the time I would drive it. When it idles high it idles at about 1500 rpms when its out of gear in neutral. First i cleaned the IAC valve and it seemed to help for like a day or 2 then the high idle was back. Then quickly checked for vacuum leaks and everything i did check looked good (not a though check though). Then i tested the tpc and it tested good except both open and closed reading were .2 lower than what it called for but i was told it wouldn't matter. I went ahead and put in a new tpc and when i started it up it liked to idle high around 1700 and sometimes 2000 rpms, so i put the old one back in and it ran great for almost two days and then back to its old ways. Also if its idling high and i shut it off it will idle down to about 900 (normal idle for the car) and the as soon as you touch the gas and let it idle down it just goes to 1500 rpms. This problem now has me stumped and I don't know what to try next, i would appreciate an ideas or help I could get about this, Thank You.