a few weeks ago my car started to drop like 150-200 rpm every 3 seconds no matter what rpm im in. when im driving it dosent drop to much but u can feel it. then it hasent really been doing it to much but when i have my air on ac or heater the car revs up like 150-200 rpm every 3 seconds. what could it be. thanks

 

The idle air control is most likely clogged.

It may be titled idle air control but when it's messed up it affects the full rpm range.