What causes the BMW e90 to shake and stall during cold starts?

[NathanMarie]

When the BMW e90 starts in a cold state, it may experience shaking or even stalling. This is likely due to severe carbon buildup in the engine, which requires timely cleaning of carbon deposits on engine components to prevent affecting the vehicle's performance. Here are some relevant details: 1. A cold start refers to starting the car when the engine's coolant temperature is low. Under normal engine temperature conditions, if the engine can start smoothly after several attempts, it indicates the battery is in good condition. If the engine speed gradually decreases after one start, the battery needs to be charged promptly. Regular battery inspection and maintenance are beneficial for ensuring the car can start properly. 2. Generally, engine shaking may also be accompanied by piston knocking, which indicates severe wear between the piston and cylinder wall, often producing an unusually dull knocking sound. Engine malfunctions can lead to issues in the vehicle's powertrain, so it's important to monitor the engine's operating condition closely.