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Hello..I have a 1996 Z26 3.1 and I have some serious idle problems. The minute you start the car it jumps up to like 1800 rpms (normal is about 500 rpms) and stays that way. I have to kill the engine and restart a couple times in order for it to tone down so i can shift into Drive and go on about my way without ruining my transmission. I replaced the Air Idle Control Valve already (old one was black and had carbon buildup....when comparing the new and old it seemed like the spring in the new one came out further than the one in the old one) and it acted fine for about 2 weeks at most. I looked online for some info and heard that maybe AICV was faulty cuz it was the cheapy one at Auto Zone and so I took it back and cleaned the old one and put it back in there and now it still runs high but doesnt do it as much. I don't know what else it could be. Its wierd....I mean when you start it, it will jump way up then it MIGHT jump down then back up then down. I replaced the Throttle Positioning Sensor FIRST OFF but when I started the car it acted the same so I took it back and got the new AICV. I dont know what else to do...HELP!!! Its drinking up my gas and probably not good for my brakes or anything else for that matter. Any help or information would be much appreciated. Thanks

just a couple of possibilities-by no means gauranteed to be it.....it could be a vacuum problem,so check your vacuum line connections,and lines for leaks.
 

If no codes are being thrown it could also be the ecm itself.
 
You may also want to try another new air idle valve-just to be sure,one way or the other.
 

Also trace the wireing from the throttle position sensor --i had a weird idle similar to this on my lumina a couple of years ago and it turned out to be a bare wire in this circuit touching at times a bare wire next to it in the wireing harness a good ways back in the harness where it sat under the alternator bracket...mind you,that was the lumina 3.1 -but my point is-check that wireing if you don't find the trouble in  the mean-time.

Dont these 3100 have probems with intake manifold gaskets leaking?  If all your vacuum lines look fine you might want to try checking the intakes by spraying some brake cleaner where they bolt together and listen for changes in idle.