What Causes the Car Body to Shake During Ignition?

[McMackenzie]

There are several reasons why a car may shake suddenly during ignition: 1. Poor fuel quality: In winter, the lower temperatures make it difficult for the fuel to atomize when starting a cold engine, leading to insufficient mixing of fuel and air in the cylinders, which causes difficulty in starting and severe shaking of the car body. 2. Spark plugs: The gap between the electrodes of the spark plugs gradually widens, reducing ignition energy and impairing fuel atomization. 3. Ignition coils: Aging ignition coils, high-voltage wires of the spark plugs, or electrical leakage can decrease ignition energy. 4. Carbon buildup on engine valves and intake manifold: Carbon deposits can absorb a certain amount of fuel, causing the electronic control unit to miscalculate. For example, while the unit may command the injection of 100 units of fuel-air mixture, only 90 units actually reach the cylinder. Even if the remaining 90 units burn completely, the required power output is not achieved, leading to unavoidable shaking.

[ColeLynn]

I've been driving for over a decade, and it's quite common for new cars to shake a few times during startup. The main reason could be that the engine oil hasn't fully lubricated when the engine is cold, leading to increased friction between internal engine components, especially noticeable in low winter temperatures. New engines require a break-in period; during the first few thousand kilometers, the piston rings and cylinder walls haven't fully seated, causing higher startup resistance and resulting in shaking. Additionally, check the fuel quality—poor fuel can lead to incomplete combustion and shaking. If the shaking persists and is accompanied by unusual noises, it might indicate improperly installed engine mounts or issues with the spark plugs. It's advisable to report this during the first maintenance visit to the 4S店 (dealership) and have them check the engine data stream with a diagnostic tool, which should generally resolve the issue.

[MacKendra]

As an engineering-minded individual analyzing new car startup vibrations, the root cause lies in unstable internal engine torque. During the startup moment when the crankshaft position sensor signal hasn't stabilized, the ECU's fuel injection control may have minor inaccuracies. Particularly in direct injection engines, poor fuel atomization during cold starts leads to mixture concentration fluctuations that cause shaking. New cars have tighter assembly tolerances, and excessive belt tension can also induce vibrations. My recommendation is to warm up the engine for 30 seconds before driving off. If severe shaking occurs consistently, remember to record video evidence and visit the dealership to check ignition coil resistance values and high-voltage pack voltage. These issues are covered under the new car warranty period and can be addressed free of charge, so no need to worry.

[BarrettFitz]

It's normal for a new car to shake a few times when starting up. My car did the same in the first six months. After running 20,000 kilometers, it actually became much more stable - this is essentially the engine breaking in. However, it's important to distinguish between normal and abnormal shaking: slight vibration is normal, but if the entire body noticeably rocks, you should pay attention. Focus on checking three things: whether the spark plug electrode gap is too wide, if the battery voltage is stable, and whether there are impurities in the fuel tank or fuel lines. Remember not to park on slopes for extended periods, as oil drainage can cause insufficient lubrication during startup, leading to shaking. Just have the technician tighten the engine mount screws during each maintenance service.

[VanDylan]

When you first get your new car, the most concerning issue is often the engine shaking upon startup, making you suspect there's a problem with the engine. In fact, 90% of the time, this is a normal phenomenon caused by residual air-fuel mixture in the fuel system. It improves significantly after the first oil change. Note that if the car sits for over a week before starting, it's more likely to shake because the oil has mostly drained back to the oil pan. Occasional slight shaking is nothing to worry about, but if it shakes violently every time you start the car, you should check for issues like an intake manifold leak, a stuck carbon canister purge valve, or abnormal fuel pump pressure. There was a case in our car owner group where the shaking was caused by interference from the anti-theft system—disconnecting the battery to reset the ECU solved the problem.