Idle speeds up/slows down
 

I've only noticed this recently... when my car is idling at 750 or whatever I have it set to.. it slows down for a few seconds, and goes back up to 750, and my interior lights go dim as its slowing down, and my battery meter goes down just during the slow part, then just goes back to normal when it speeds up..
Anyone have any ideas?

check your battery and alt

Forgot to mention, the lights dim ever so slightly, hardly noticeable.. even when i hold my foot down at 2k RPM, it slows down a little and goes back up to 2k without moving my foot

anyone have any ideas except battery/alt? the power drop is not huge