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. Ford Mondeo V Hatchback (CE) (2014/09-X) Ford Mondeo V Turnier (CF) (2014/09-X) Ford Focus III (2010/07-X) Ford This Part Fits the Following Vehicles Model Ford Mondeo V Hatchback (CE) (2014/09-X) Ford Focus III (2010/07-X) Ford FOCUS III TURNIER (2010/07 - X) FORD FOCUS III SALOON (2010/07 - X) FORD C-MAX II (DXA/CB7, DXA/CEU) (2010/04 - X) FORD S-MAX (CJ, WA6) (2015/01 - X) FORD GALAXY (CK) (2015/01 - X) FORD KUGA II (DM2) (2012/05 - X) VOLVO V70 III (135) (2007/04 - X) VOLVO V40 HATCHBACK (525, 526) (2012/03 - X) VOLVO V60 I (155, 157) (2010/07 - X) VOLVO S60 II (134) (2010/04 - X) VOLVO S80 II (124) (2006/03 - X) FORD USA MUSTANG COUPE (2014/02 - X) FORD USA MUSTANG CONVERTIBLE (2014/02 - X)