What causes unstable idle speed when the BMW N52 engine is cold?

1 Answers
EliasFitz
07/29/25 8:24pm
BMW N52 engine unstable idle speed when cold is caused by the following reasons: 1. Dirty throttle body: Excessive carbon buildup in the throttle body directly leads to unstable engine idle speed and poor acceleration. 2. Excessive carbon deposits: Too much carbon buildup inside the engine reduces combustion chamber volume. Additionally, the heat-absorbing nature of carbon deposits can cause incomplete combustion in the combustion chamber, increasing the likelihood of knocking and engine vibration. 3. Engine misfire: Poor spark plug ignition or insufficient fuel injector atomization results in incomplete combustion or complete non-combustion in the cylinder, causing more severe vibration. 4. Poor fuel quality: Low-quality fuel directly affects combustion efficiency. Low octane rating is the main cause of engine knocking. 5. No warm-up: Starting the car directly without warm-up means engine components haven't received proper oil lubrication.
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