What Causes the Shaking When the BMW 5 Series Start-Stop Function Activates?
2 Answers
Shaking when the BMW 5 Series start-stop function activates may be due to severe engine carbon buildup. Below are the specific causes and solutions: 1. Specific Causes: A common reason for car shaking is a dirty throttle body or excessive carbon buildup in the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts. This makes starting difficult. After the engine starts, gasoline is then sucked into the cylinders by the engine's vacuum, making the mixture too rich. The fluctuating air-fuel mixture causes idle shaking after a cold start. Excessive carbon buildup can affect the smoothness of cold starts. 2. Solutions: Clean the fuel system and check whether the idle air control valve has carbon buildup—it should be cleaned if necessary.
My BMW 5 Series shakes severely during start-stop activation, which could be due to several common reasons. The engine vibrates more during ignition, especially when the spark plugs are aged with uneven gaps, leading to decreased ignition efficiency and causing shaking. Another issue could be with the starter motor; frequent start-stop cycles wear out the motor gears, resulting in rough starts. Battery condition is also crucial—when voltage is unstable, the system startup becomes noticeably shaky. There might also be a software bug where the ECU's start-stop control logic is disrupted, requiring a firmware update. Additionally, worn or broken engine mount bushings reduce vibration damping, transmitting shakes into the cabin. It's advisable to conduct a thorough inspection first, try replacing the spark plugs, or disable the start-stop function at traffic lights to avoid discomfort. Prolonged shaking may damage engine components, so early repairs are safer.
