1. Because during the operation of the EFI engine, a small part of the exhaust gas generated by combustion in the cylinder will generate carbon deposits at the throttle body through the intake valve and the intake pipe.

2. After the air passes through the air filter, impurities will remain in the throttle valve.

3. When the car is used for a long time, it will form dirt at the throttle body, which will cause the low-speed throttle to be disobedient and difficult to start the cold car.