A 2011 Volkswagen Golf 6 1.4TSI car with a mileage of about 30 thousand km. User response: when the vehicle is running, the engine sometimes loses its strength. After receiving the car: first test the car to confirm the fault phenomenon, indeed as the customer described. Connect VAS5052A to check vehicle related electrical control system, read the fault code is: 00665 - boost pressure control has not reached the control limit static. It is normal to check the external pipeline of the turbocharger according to the fault code, and the connection of the turbocharger pressure limit solenoid valve (N75) and the turbocharger air recirculating solenoid valve (N249). Check the engine data flow 115 sets of boost pressure data. When the engine speed is at 3000 r/min, the display value is only 1.1 bar (1 bar=105 Pa), and the standard is 1.6 bar 1.8bar. A special tool VAG1390 manual vacuum pump is used for static test of turbocharger. The manual vacuum pump is operated repeatedly. When the pressure is 300 mbar, the transmission rod of the pressure tank begins to move. When the pressure reaches 750mbar, the transmission rod stays at the adjustment end position. It is normal. When the pressure is released, the transmission rod is not completely restored to the closed position of the bypass valve, and it is not normal. Remove the turbocharger and remove the drive rod pin. It is found that the bypass valve shaft is seriously loose and rotated inflexibly, often unable to return. Troubleshooting: commissioning after replacement of turbocharger, troubleshooting thoroughly.