Why does the tachometer suddenly increase when stepping on the clutch?

[GrantLynn]

The reasons for the sudden increase in the tachometer when stepping on the clutch are as follows: 1. Normally, when shifting gears, you simultaneously step on the clutch and release the accelerator. The moment the power is cut off, the engine speed begins to drop. If the accelerator is released too early, the engine speed may drop first, potentially causing engine braking and resulting in a jerking sensation, as if suddenly stepping on the brakes. If the accelerator is released too late after the clutch is disengaged, continuing to press the accelerator with no load on the engine will inevitably cause the speed to rise. 2. Since the vehicle is in motion, the idle speed will be slightly higher due to the ECU's idle compensation function. When the clutch is pressed, the engine is relieved of its load, and the operating resistance instantly decreases, causing the engine's rotational force to increase and the speed to rise. This is similar to pulling an object forward with a rope and suddenly cutting the rope, causing a sudden forward jerk. Once the speed rises beyond the target idle speed, the ECU intervenes to restore the idle speed to the target level for the current operating conditions.