Is it normal for a BMW to occasionally stall at a red light?
2 Answers
Not necessarily. New BMW models are equipped with engine start-stop technology. When you stop at a red light by pressing the brake and shifting to N gear until the vehicle comes to a complete stop, the engine automatically shuts off. When the light turns green, shifting to D gear and pressing the accelerator will directly restart the engine. If the engine starts normally when pressing the accelerator in D gear after stalling, then it's functioning as intended. However, if you need to manually restart the engine, it's advisable to visit a professional repair shop. The automatic engine start-stop system is designed to shut off the engine temporarily during stops (e.g., at a red light) and automatically restart it when it's time to move forward. Its English name is STOP&START, abbreviated as STT. The STT intelligent fuel-saving system is a set of controls for engine start and stop. It works by integrating an enhanced motor with idle start-stop functionality into a traditional engine, allowing the engine to completely shut off when idle stop conditions are met. When the vehicle needs to move forward again, the idle start-stop motor system quickly responds to the driver's command, rapidly restarting the engine for seamless operation, thereby significantly reducing fuel consumption and exhaust emissions. STT stands for STOP&START. The STT intelligent fuel-saving system is a set of controls for engine start and stop. The system uses a computer to determine the vehicle's status, such as during stops at red lights or in traffic jams. The computer can automatically stop the engine while maintaining the operation of in-car systems like air conditioning and audio. This technology can save approximately 5% of fuel under normal driving conditions and up to 15% in congested traffic. According to authoritative tests, this technology can help an average car save 10% to 15% of fuel annually.
I've been driving a BMW for over five years, and occasional stalling at red lights is indeed abnormal, indicating unstable engine idle speed. Common causes include carbon buildup obstructing air intake, a dirty throttle body affecting the air-fuel ratio, or aging ignition coils causing misfires. My own car had the same issue before, and cleaning the throttle body and fuel injectors solved it. If it happens frequently, you should also check whether the fuel pump pressure is sufficient and if there are any vacuum leaks. German cars have higher maintenance requirements; it's recommended to perform an intake tract cleaning every 20,000 kilometers and replace spark plugs promptly. Ignoring such minor issues may damage the oxygen sensor or even the catalytic converter, and repair costs would then be much higher.
