Engine revs at idle

Ive noticed that my car will sometimes rev up about 200 rpms and then back down and then back up when it's idling. Does anybody know what could be causing this?

Its a 91 Nissian Pulsar

Could be any number of things... ac compressor turning on/off, thermostat opening, a senser acting up. Probly no big deal.

hmm I hope your right jonwell. I just bought this car 2 weeks ago and I'd hate to have to pay for a major repair already.

Doubtful that anything major would cause that. Last time I had a similar problem it was a a loose EGR tube going into the intake. Look possibly for any leaks into the intake past the mass air meter. The mass air meter is reading a certain amount of airflow, but more air is coming from somewhere and the computer compensates back and forth.

ya, could be that. I'd be more worried if it were suddenly bogging down a few hundred rpm though, not the other way around.

vacuum leak

Jonwell is correct. In some cars, you will also feel the brake pedal go down a bit when the vacuum changes as the IAC valve adjusts to engine loading at idle.