I drive a 1991 Mitsubishi 3000gt SL N/A. I noticed the idle was a bit high fluctuating between 2500RPM and 3000RPM, so I decided to take a look at the IACV. There was power going in from the harness to the valve (12.3 Volts) an the resistance on the actual valve read 0.04 Ohms. When I removed the valve from the vehicle and turned the key from the On to the Off position, the shaft of the IACV did not move back and forth like it was supposed to. So I went to O'Reilly's and bought a new IACV, put it on, but the idle stayed the same. I returned the new valve, put back in the old one, and somehow I disconnected the MAF from the air cleaner box. Needless to say, when I put everything back together and turned on the car, the RPMs jumped straight to 5000, at idle. Help

 

Replace the camshaft sensor, that happened to me and i couldn't rev past 3000RPM's and it did the trick. its not the transmission and not the engine so its definitely some electrical gremlin, or at least it has been for me.

 

Had to reset ECU so it could relearn the MAF sensor. It turned out to be a faulty idle adjustment screw, the one on the top of the throttle body. When I went to adjust it, it broke in half. Replaced it and now my idle is at ~900 rpm.