1. Faulty ignition switch: inspect the ignition switch to ensure it is not stuck in the "on" position.
2. Fuel injector problem: a faulty fuel injector can cause the engine to continue running even after the ignition switch is turned off.
3. Fuel shutoff valve failure: the fuel shutoff valve is responsible for preventing fuel from reaching the engine when the ignition is turned off. Failure of this valve can lead to run-on issues.
4. Electrical issue: a short circuit can cause unintended power supply to the ignition system, making the engine continue running.
5. Faulty vacuum modulator: in diesel engines with automatic transmission, the transmission and engine are interconnected through a vacuum modulator. If the modulator is malfunctioning, it may affect proper shutdown.
6. Stuck butterfly valve: some Mercedes models have butterfly valves in the intake system to regulate airflow. A stuck valve can prevent the engine from getting the proper air/fuel mixture for efficient combustion and can lead to run-on.
If you are unable to identify the cause, it is advisable to seek the assistance of a professional mechanic for proper diagnosis and repair. Attempting to diagnose and fix complex engine issues without the proper knowledge or tools can lead to further damage or safety risks.
