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 BMW All All N55 3.0L BMW E70 X5 S63 4.4L BMW E70 X5 M S63 4.4L BMW E71 X6 S63 4.4L BMW E71 X6 M S63 4.4L BMW F10 M5 S63 4.4L BMW F13 M6 S63 4.4L