please help

ok so when i am sittin still at a red lite or in a drive thru or whenever my car will start revving up. i dont no wuts goin on!! like my rpm's will just rev up and down with about a 500 rpm difference!! people always think im reving my engine but its doing it all on its own!! can someone please tell me what the hell is goin on?

Is it doing it when your AC is on? It could just be the idle raising once the AC kicks in.

Could be a sticking IAC valve as well.