idle erratic

everynow and then my lude starts idling erratically. it goes up 1rpm then down an 1rpm constantly. if i turn the car off and back on it stops doing that. any clue why it does this?

My '86 Prelude Si does this, but it happens every day. I'm told it is the Idle Air Control Valve, aka Fast Idle Valve. On my car, it's supposedly located near the air intake on the engine. Down where the air filter plumbing connects with the engine. I found the part for $50, but every car is different. My dealer says they are easy to replace. I just need the cash to fix mine...

Good luck.