If the throttle is closed while the engine is overrunning, back pressure will develop in the compressor housing due to the constant pressurization. This back pressure significantly reduces the speed of the compressor impeller, with the ultimate result of reduced boost pressure and increased turbine lag. To avoid this, the turbocharger shunt air valve is opened by an electric actuator. The valve opens a bypass pipe that allows compressed air to rotate through the compressor blades back to the intake side of the compressor loop. In this way, the required turbine speed is maintained. When the throttle opens, the turbocharger shunt air valve closes and the booster pressure is immediately available. This Part Fits the Following Vehicles Make Model Submodel Engine Audi A3 8P FWD 2.0T Audi A3 8P Quattro 2.0T Audi B7 A4 FWD 2.0T Audi B7 A4 Quattro 2.0T Audi B8 A4 FWD 2.0T Audi B8 A4 Quattro 2.0T Audi B8 A5 Quattro 2.0T Audi B8 Allroad Quattro 2.0T Audi C7 A6 FWD 2.0T Audi Q5 Quattro 2.0T Audi TT MKII FWD 2.0T Audi TT MKII Quattro 2.0T Audi TTS MK2 (2006-2013) 2.0T Volkswagen All All 2.0T Volkswagen All All GLI