What causes the BMW e66 to shake during cold starts?

[McMiles]

BMW e66 cold start shaking is caused by the engine temperature being too low, or the air-fuel mixture being too lean or too rich. Engine temperature too low: One issue faced during cold starts is low temperature, especially in cold northern regions. If the spark plug gap is too large and the ignition energy is insufficient, it can easily lead to ignition failure, causing individual cylinders to misfire and resulting in shaky starts. Air-fuel mixture issue: Cold start shaking can also be caused by the air-fuel mixture being too lean or too rich. The problem with the air-fuel mixture might be due to a fault in the closed-loop control system. Since the exhaust pipe temperature hasn't reached the required level during cold starts, the oxygen sensor may not have reached its operating temperature or could be damaged, leading to cold start shaking issues.