R Klasse reduced engine power

Reduced engine power and a check engine light often point to issues within the engine management system. A defective throttle valve is a plausible cause, especially given the symptoms you describe. The throttle valve, or throttle body, controls the amount of air entering the engine. A malfunction can indeed trigger limp mode, which is a safety feature that limits engine power to prevent further damage. A response delay from the throttle body can also indicate that the module is not working correctly. It's possible the accelerator pedal module is faulty, but problems with the throttle body itself are more common. Has the car been scanned for diagnostic trouble codes (DTCs)? This would give a clearer indication of the fault.

Thanks for the quick reply! I haven't scanned for any codes yet, but that's a good point. I'll get that done ASAP. If it does turn out to be the throttle body, what kind of replacement cost am I looking at, roughly? Also, is there anything else I should be checking before I jump to replacing the whole thing?

The replacement cost can vary depending on whether you opt for a new or remanufactured throttle body, and labor rates in your area. Without knowing the exact diagnostic code, it's difficult to pinpoint the repair with certainty. However, assuming the diagnostic trouble code points directly to the throttle body, a replacement should resolve the issue. Before replacing it, inspect the wiring harness and connector leading to the throttle body for any signs of damage or corrosion. A loose or corroded connection can sometimes mimic the symptoms of a faulty throttle body. If the wiring appears to be in good condition, then replacement is likely necessary. Considering the potential complexity and the need for diagnostic tools, consulting a workshop would be advisable.

Just wanted to give the situation. I took your advice and got the car scanned. It turns out it was indeed the throttle valve. I took it to a local workshop, and they replaced it for 265€. The car is running much better now – the engine power is back, and the check engine light is gone. Thanks for the help!