635 csi rpm problem

my BMW 635 csi won't go over 2500 rpm under load. when in neutral and not moving the engine rpm will go over 2500 but on the road they won't. i'm afraid as its a sensor but i'm trying to avoid that. any other suggestions as to what would cause this problem?

Your problem is most likely the air flow meter. It gets coroded on the inside. Check out this forem, it will guide you thru the repair procdure.
www.normgrills.net/bcg/injection