Why does a new car shake severely during cold start?

[LucilleMarie]

Reasons for severe shaking during cold start: 1. Low ignition energy causing vibration. When the engine temperature is too low, both fuel and lubricant temperatures are low. During cold start, a richer air-fuel mixture is required, which in turn demands higher ignition energy. Excessive spark plug gap or aging ignition coils/high-voltage coils can all lead to decreased ignition energy, resulting in vehicle shaking. 2. Incorrect air-fuel mixture ratio causing cold start vibration. When certain engine sensors provide significantly erroneous signals, the ECU makes incorrect judgments, leading to errors in fuel injection timing and ignition timing control, which manifests as engine shaking. 3. Uneven cylinder conditions causing engine vibration. In multi-cylinder engines, significant differences in ignition energy between cylinders may occur. Additionally, varying degrees of piston and piston ring wear result in inconsistent compression ratios, causing uneven power output and engine shaking.