After a drive home from work (25 miles, 20 of which on the highway) my 08 coupe makes a distinct rumble and at idle the rpms dip for some reason. i think its something to do with the car not being able to cool itself properly because sitting at idle the radiator fans go crazy after about 5 min. No idea whats going on, if someone can help shine some light on this.

 

Try cleaning the throttle bodies.