My prelude has developed a problem over the last year or so that has become annoying. At first when the weather turned cold, the card would start revving at idle. It would alternate anywhere between 500 and 2000 until i starting moving. when i stopped again, it started again. a mechanic friend of mine tightened a bolt just below the throttle plate. he said that this spring loaded screw would back out from time to time causing this. He put some locktight on the screw and set it in a few turns. it worked for a time. then when the weather changed again, the problem returned. I'm not sure what is happening. any ideas?

 

IAC valve

 

thanks

 

Would have to second that, look around online they have a way you can test that with a multi meter