My next door neighbor has a 94 Prelude Si. When he starts his car it just revs up and down constantly. I looked at it and couldnt find any vaccum leaks. He said it just started on Christmas eve. When he drives the car it runs fine though. I was thinking it was maybe the idle/air sensor or something that needed to be cleaned. If anyone knows what to do please let me know. I told him I would try to help him out on it.