Why does the Audi A6L experience idle shaking during cold starts?

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Audi A6L cold start idle shaking is mainly caused by: 1. The engine temperature is too low. Both fuel and lubricant temperatures are low during a cold start, requiring a richer air-fuel mixture. A richer mixture demands higher ignition energy. If the spark plug gap is too wide or the ignition coil/high-voltage coil is aged, it can lead to reduced ignition energy, causing the car to shake. 2. Uneven cylinder conditions. In multi-cylinder engines, significant differences in ignition energy between cylinders, or varying degrees of piston and piston ring wear leading to inconsistent compression ratios, can result in uneven engine power output and shaking. 3. Incorrect air-fuel mixture ratio. During cold starts, if certain engine sensors or their signals have significant errors, the ECU may make incorrect judgments, causing inaccuracies in fuel injection timing and ignition timing control, leading to engine shaking.