Why does an automatic transmission car shake when starting?
2 Answers
The most common cause of car shaking is a dirty throttle body or excessive carbon deposits on the fuel injectors. If an automatic transmission car shakes when starting but runs normally afterward, it may be due to the following reasons: 1. The throttle body is too dirty, causing uneven air intake and resulting in shaking. 2. Poor fuel flow, leading to insufficient fuel supply at low throttle and uneven operation of engine cylinders, causing shaking. 3. Abnormal transmission operation. 4. Broken or burned high-voltage wires or spark plug failure in one cylinder, causing unstable engine operation and shaking. 5. Check if the battery voltage is within the specified range.
Having driven automatic transmission cars for twenty years, the most common cause of shaky starts is a malfunction in the transmission system. Particularly, when the torque converter or clutch plates are worn out, the engine's power delivery becomes uneven, causing the car to shake uncontrollably like a seizure. Another possibility is dirty or insufficient transmission fluid, leading to slipping friction plates; in severe cases, even an imbalanced driveshaft can contribute to the problem. If you feel unsteady starts while driving, avoid forcing it further—I've seen many cases where prolonged neglect leads to complete transmission failure. During regular maintenance, remember to check the fluid quality and replacement intervals; typically, changing the fluid every two years or 40,000 kilometers can prevent such issues, saving both hassle and money.
