Mercedes C Klasse rough running and power loss resolved

Sounds frustrating. I had similar symptoms on my old Saab 9-3 Check engine light, rough running, hesitation. In my case, it was a faulty oxygen sensor messing with the air-fuel ratio. The car was compensating and running lean. Have you checked your O2 sensors? A faulty EGR valve could also cause similar issues by affecting the combustion process.

Thanks for the quick reply O2 sensors, huh? That's a good point. I haven't specifically checked them with a multimeter or anything. Where are they usually located, and is there a way to test them properly without specialized equipment? What did you end up doing with your Saab?

The O2 sensors are typically located in the exhaust system, before and after the catalytic converter. Testing them properly usually requires a multimeter and knowing the expected voltage ranges. Without proper testing equipment it is difficult to diagnose properly. I ended up taking my Saab to a trusted workshop. They ran diagnostics, confirmed the faulty sensor, and replaced it. Considering your symptoms and the potential for damage to the catalytic converter if it's running lean for too long, I'd recommend getting it professionally diagnosed to avoid further issues.

Okay, appreciate the advice. I think you're right; I don't want to risk damaging the catalytic converter. I'll take it to the workshop. They ran diagnostics and found out that indeed an injection valve was defective. Replacement including labor cost me 515€. Runs great again now Thanks again for pointing me in the right direction