Why does the car shake when starting?
2 Answers
Car shaking during startup can be attributed to the following reasons: During a cold start, the internal operating resistance of the engine is very high, so the ECU injects more fuel, which can cause some shaking. When the oxygen sensor hasn't reached its operating temperature during a cold start, it can also lead to engine shaking. If the engine has a misfire (missing cylinder), it disrupts the smooth operation of the engine, resulting in shaking during a cold start. Some engines are particularly prone to carbon buildup; excessive carbon deposits in the engine can also cause shaking during a cold start. After a cold start, the engine temperature is relatively low. To quickly bring the engine up to operating temperature, the ECU controls the fuel injection system to inject more fuel, which can cause some shaking. This is normal.
I've driven many cars, and the most common cause of shaking during startup is aging spark plugs or carbon buildup issues. They are responsible for ignition; if worn out, the engine won't ignite smoothly, causing severe shaking during startup. This is more noticeable in winter when fluids flow slower due to the cold. Clogged fuel injectors or insufficient fuel pump pressure can also cause this, leading to uneven gasoline spray. I remember my previous car's steering wheel shaking so badly during startup that my hands went numb—it improved after replacing the spark plugs and cleaning the fuel system. Loose engine mounts are another reason; these are the cushioning pads that secure the engine, and if they age and loosen, they can cause shaking. Long-term neglect can increase internal engine wear and lead to bigger problems, so I recommend checking the fuel system and ignition components at a repair shop as soon as it happens. Regular maintenance is key to prevention, such as replacing spark plugs every 20,000 kilometers.
