idle, and poping

i have the irratic idle when i start the car it's fine but after i get the rpms over 4 grand and i stop at a light the idle goes from 1 grand to 1500 up and down every time i stop and like 5 mins after i start drivin my car feels like it is losing power and i hear poping noises coming from my intake like it's backfiring what can be wrong?