What Causes Low-Speed Jerking?
2 Answers
Transmission jerking is the impact sensation caused by the inertia of moving parts inside the engine. Below are the reasons for engine jerking: 1. Causes of engine jerking: During the process where the engine speed is either increased or decreased, if not handled properly, sudden changes in engine speed during gear shifts can cause the inertia of the engine's moving parts to react against the vehicle body. 2. Low-speed jerking: Many drivers experience this issue. When driving at low speeds, the gear frequently shifts between first and second, and the clutch repeatedly engages and disengages. If power transmission cannot be smoothly completed within a short time, common low-speed jerking occurs. Jerking sensations are normal during startup and low-speed driving, usually due to turbocharger engagement at low RPMs, which affects engine speed. 3. Upshift jerking: This is mostly caused by the transmission's response speed being insufficiently fast. The upshift speed cannot keep up with the throttle input, so the jerking sensation occurs at the moment of gear shift. 4. Downshift jerking: This is mostly due to the intervention of the energy recovery system. Once the driver releases the throttle pedal or presses the brake pedal, the generator immediately starts working, placing additional load on the engine. This affects the engine speed, causing it to be out of sync with the clutch plate speed, resulting in a jerking sensation.
Yesterday while repairing a car, I just dealt with one that had severe jerking issues. I found that low-speed jerking problems are usually related to three aspects. First is the fuel system—clogged fuel injectors can cause unstable fuel supply, especially common in older cars. Second is the transmission fluid; when the fluid hasn't been changed for 70,000 to 80,000 kilometers, the clutch plates are prone to slipping. Additionally, sensors like the mass airflow sensor, if coated with sludge, can cause the ECU to misjudge the air intake, leading to jerking. I recommend checking these three areas first—in my experience, 80% of such cases are due to these reasons.
