RPMs going up/down ?

[GAdriver]

my friends 92 prelude with an h23 used to idle up and down from 1k to 2.5k back and forth when ever it wanted to. Now it does it constantly up/down up/down. What could be the problem??

 

[Enigma_Man]

It could be any number of things man, that's a very very vague description of a car not many of us are going to be familiar with.

But in general, here's things to check:

airflow sensor
intake leak (if it uses a MAS, and not manifold pressure)
temperature sensors
throttle plate / cable / return spring
throttle position sensor
cold start solenoid
blah
blah
blah

-Jesse