Why does a sedan jerk when starting?
2 Answers
Starting with a jerking sensation may be due to dirt and impurities inside the transmission. These contaminants accumulate in the valve body, forming blockages that prevent effective regulation of oil pressure, leading to jerking impacts. Alternatively, it could be caused by factors such as clogged engine oil passages. Below are specific reasons for the jerking sensation during startup: 1. It is normal for an automatic transmission car to jerk during startup. When you want to accelerate quickly while driving, you need to press the accelerator deeply. At this point, the automatic transmission will automatically downshift to increase the engine speed. Once the speed reaches a certain level, it upshifts again. After upshifting, the speed will drop noticeably, resulting in a relatively pronounced jerking sensation. The automatic transmission's decision to shift gears is closely related to the overall powertrain conditions, including engine speed, driving speed and resistance, and throttle depth. If the timing of the gear shift is not well managed, a jerking sensation will naturally occur. 2. Clogged oil passages in the car's engine can also cause jerking. The engine's ignition, air intake, and fuel injectors collectively determine fuel combustion, which is the source of the engine's power. If the air intake decreases, the ignition weakens, or the fuel injection reduces, the power output will be insufficient, leading to a jerking sensation.
After driving for so many years, I've found there are quite a few reasons for jerky starts. The most common one is worn clutch plates, especially in older manual transmission cars where worn clutch plates can cause uneven power delivery, making the car jerk when you step on the gas. Another reason could be the need for transmission fluid replacement—if the fluid in an automatic transmission is dirty or low, the control components respond sluggishly, leading to jerky starts. Driving habits also play a key role; some beginners press the accelerator too abruptly or start driving before the engine has warmed up, putting excessive load on the engine. Additionally, faulty spark plugs or unstable fuel pump supply, particularly during cold starts, can contribute to this issue. I recommend cultivating smooth driving habits, avoiding sudden acceleration, and regularly checking the clutch or transmission fluid during maintenance to minimize these problems. Jerky starts aren't just uncomfortable—ignoring them long-term can damage vehicle components and compromise driving safety.