I have a 92 vx that has a swap out of a 94 gsr. When i start it it revs to 3k rpms for 5-10 second then drops suddenly and starts reving up and down. When it warms up it idles at 1500-2000 rpms and sometimes will rev up and down but with fewer rpms. I have already replaced the iacv and pull timing cover to make sure that everything was lined up properly. It just started doing this about a week ago and the motor has been in my car for about 2 months. I have also checked everywhere for vaccum leaks. The fan comes on and the car does not runs hot. I have a code 1 cel for o2 sensor, so i ordered one and i am putting it in tomorrow but, everyone i have talked to says that it is unlikely that the o2 is causing it to run like that. Only mods are CAI, header, and exhaust.

Any ideas????

p.s. Also pulled the throttle body and cleaned with intake and throttle body cleaner w/ toothbrush.

 

Nevermind...it was the fast idle thermo valve. I had to tighten the plastic ring.