Vag engines need recirculating dump valves. If you put on an atmospheric dump valve it will make your car go nuts. My mate has a 1.8T (audi TT) engine in a Mk1 GTI, he has a stand-alone ECU and a forge bailey dump valve. Works fine with the stand alone ECU but wouldn't work well with a normal ECU with the normal airflow sensor. This is all from his mouth, so if Ive been spouting crap for the last couple seconds, i apologise!