When I have my defrosters on and the car at normal idle, after like a minute with the defrosters on my idle starts to pulsate going up and down up and down. Not to high or to low, goes from like 900/800 to about 600/700 and goes back and fourth.

Is this normal? Or how do i fix it?

 

Sounds bac related...

 

The defroster (rear hatch????) on, there is an electrical load put on the engine. The bac should compensate for the load. It sounds like it's trying to do that. Maybe remvove the bac and clean it out with some carb cleaner???????? Don't damage the piston.