Car runs good but at 1500-2500 Ron's if I keep throttle steady there is a maybe 100-200 rpm surge happening every second or so. Is it a vacuum leak or maybe the diverter valve? It's a 04 1.8t fwd. has apr stage 1. No cel have been thrown. Doesn't miss a beat under throttle but once it settles out it starts the surging. Any help is appreciated. Thanks guys these German cars are a little intimidating.