Hey i installed an amp and a sub. When I'm jamming out and the car is stopped or in park the RPMs goes from 600 to 900. just when the system is blasted.

I have an 800w ken wood and one 12" bridge

Let me know if you guys ever happen to you and what will fix it

 

my guess is the Increased load placed on the Alternator combined with an Idling engine causes the ECM to raise Idle Speed Slightly to compensate.

just a Theory.....i've seen this only once before.