Why does the tachometer pointer swing after the cold car starts?

After the cold car starts, the pointer of the tachometer swings, which is generally caused by carbon deposition on the accelerator of the car. The following are the related reasons that affect the pointer jump of the tachometer: 1. Excessive carbon deposition in the engine leads to instability of the tachometer. In most cases, it is caused by excessive carbon deposition in the throttle, fast motor, intake valve, combustion chamber and fuel nozzle of the engine. 2. Clutch and sensor failure: When the engine is controlled by ECU, the computer will continuously collect signals from various sensors. Once there is a problem in controlling the fuel injection quantity of the engine during gear shifting, refueling and oil collection, the computer program will be disordered and the speed will be unstable. 3. Problems related to the carbon canister: Problems with the carbon canister or the electromagnetic valve of the carbon canister will lead to too rich mixed gas at the start, which will also lead to difficulties in starting.