Mercedes CLA diesel engine issue

I had a similar experience with my CLA. Check engine light, engine stalls, and reduced power strongly suggest a fuel delivery problem. In my case, the issue stemmed from the high-pressure fuel pump. Have you noticed any unusual noises coming from the engine bay, particularly during startup? Have you checked the fuel filter recently? A clogged filter can mimic the symptoms of a failing fuel pump by restricting fuel flow. It might be worthwhile to check your car sensors too. Do you have access to an OBDII scanner to read any diagnostic trouble codes (DTCs) that might be stored in the engine control unit (ECU)? These codes can provide valuable information. I remember my fuel economy taking a significant hit, and the rough idling was very frustrating.

I have not noticed any unusual noises, and I have not checked the fuel filter. I do not have an OBDII scanner. Given your experience, is it likely the high-pressure fuel pump? Is there anything else that could be causing these symptoms, or is it best to take it to a workshop?

Based on your description and my past experience, the high-pressure fuel pump is a strong possibility. Other potential causes could include faulty fuel injectors or a malfunctioning fuel pressure sensor, but those are less likely given the severity of your symptoms and the intermittent stalling. Given that you do not have an OBDII scanner to confirm the DTCs, I would advise against attempting any repairs yourself. It is best to take it to a qualified workshop for a proper diagnosis and repair. They will be able to perform a fuel pressure test and use diagnostic equipment to pinpoint the exact cause of the problem. I understand it's frustrating, but that’s the safest course of action to avoid further damage. I ended up needing a replacement, and I recall it involved recalibrating some of the car sensors.

I appreciate your advice. I took the vehicle to a certified Mercedes workshop, and they confirmed that the fuel volume regulator was indeed defective, which they attributed to a failing high-pressure pump. The total repair cost came to 1510€. Thank you again for sharing your experience; it helped me to better understand the potential issue before seeking professional help.