What Are the Main Causes of Severe Engine Shaking When Cold?
2 Answers
There are several major causes of severe engine shaking when cold: carbon deposits, weak ignition, low cylinder pressure, and substandard fuel. The reasons for cold engine shaking can be summarized into the following three points: 1. Low ignition energy at low temperatures: The temperature inside the engine is insufficient, and both the fuel and lubricating oil are not warm enough. 2. Inappropriate air-fuel mixture ratio: The air-fuel mixture ratio is inaccurately adjusted, which occurs in both open-loop and closed-loop control systems. In vehicles with closed-loop control, the oxygen sensor's minimum operating temperature is 370 degrees Celsius. When starting the engine, the exhaust pipe temperature does not reach 370 degrees Celsius, so the oxygen sensor does not function, leading to ECU misjudgment. 3. Carbon deposits on engine valves and intake ports: If carbon deposits accumulate on the valves and intake ports of the engine, they can absorb a certain amount of fuel, causing the ECU to make incorrect judgments, resulting in shaking.
I've been driving for over 20 years, and severe cold engine shaking is mostly caused by excessive carbon deposits in the engine. Especially around the throttle body and fuel injectors—when they get clogged, it affects the air-fuel mixture, making the car shake like it's dancing when starting. It could also be worn-out spark plugs causing misfires and vibrations; replacing them usually solves the problem. I've experienced this a few times in my car, and changing the spark plugs fixed it. Poor fuel quality or overly thick engine oil can also contribute, as inadequate lubrication during cold starts increases metal friction. Lastly, check the engine mounts—those rubber dampeners reduce vibrations, and if they're cracked, the engine shakes even more. I recommend regular carbon cleaning and ignition system checks to prevent damage to other components.
