My car idles at around 3k when cold. After it warms up it runs up to 2.5k and then drops down to about 1.8k. It does that for a while and eventually stops at 2k and idles there. When i press the gas it goes up as normal but when i get off it drops back down to a normal 8-9 hundred rpm idle and then goes back up to 2k. I check to coolant for air bubbles and there wasn't any. I changed the IAC and that still didnt fix it. I was told by one of my friends that it could be the MAP or the O2 sensor. I just wanna know that if it is possible for one or bith of these things to cause the problem. and if it is just the O2 sensor what brand should i get. BTW its a 92 Civic DX with a d15b7

 

have you messed around with the throttle cable at all? has it always did this or did this just start all of a sudden? does the car run fine but just idles high? those questions will start to narrow the problem done

 

Fast idle air themro valve, it is under the throttle body....you can open it up and adjust it, open it up on the side that has a white plastic with a ball sticking out of the center then screw it down all the way..the back it of about half a turn or full turn.....but before you do all that test it, remove intake duct and you should see a small hole in the throttle body if you was lookin at it from the passanger side..let the car warm up and then plug it with your thumb and snap the throttle and if it runs normally then the FITV is the problem