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 8S TTRS Quattro 2.5T Audi 8V S3 Quattro 2.0T Audi A3 8V FWD 1.8T Audi A3 8V FWD 2.0T Audi A3 8V FWD 2.0T Audi A3 8V Quattro 2.0T Audi B9 A4 FWD 2.0T Audi B9 A4 Quattro 2.0T Audi C7 A6 FWD 2.0T Audi C7 A6 Quattro 2.0T Audi RS3 8V (2018+) 2.5T Volkswagen Alltrack All 1.8T Gen3 Volkswagen Atlas FWD 2.0T Gen3 Volkswagen Beetle GTI 1.8T Gen3 Volkswagen Beetle GTI 2.0T Gen3 Volkswagen Golf V All 2.0T Volkswagen Golf VI All 2.0T Volkswagen Golf VII GTI 1.8T Gen3 Volkswagen Golf VII Hatchback 1.8T Gen3 Volkswagen Golf VII Sporttwagen 1.8T Gen3 Volkswagen Golf VII GTI 2.0T Gen3 Volkswagen Golf VII Hatchback 2.0T Gen3 Volkswagen Golf VII Facelift FWD 1.8T Gen3 Volkswagen Golf VII Facelift FWD 2.0T Gen3 Volkswagen Golf VII R 4Motion 2.0T Gen3 Volkswagen Golf VII Sporttwagen Facelift 4Motion 1.8T Gen3 Volkswagen Golf VII Sporttwagen Facelift FWD 1.8t Gen3 Volkswagen Jetta V All 2.0T Volkswagen Jetta VI Sedan Sedan 1.8T Facelift 1.8t Gen3 Volkswagen Jetta VI Sportwagen 2.0T Volkswagen Jetta VI Sedan Sedan 2.0T Gen3 Gli Volkswagen Jetta VI Sedan Sedan Facelift 2.0T Gen3 GLI Jetta VI Sedan Sedan GLI Passat B7 FWD 1.8T Gen3 Volkswagen Passat B7 FWD 2.0T Gen3 Volkswagen TIGUAN MQB 4Motion 2.0T Gen3 Volkswagen Tiguan MQB FWD 2.0T Gen3