Mercedes SLC engine issues

Sounds rough. The symptoms definitely point towards combustion issues. Have you checked the knock sensor? Sometimes a faulty sensor can trigger similar problems even if the actual combustion is okay. Also, are you noticing it more when the engine is cold or hot? And what fuel grade are you using?

I haven't explicitly checked the knock sensor, but I'll add it to the list. As for when it's happening, it seems more noticeable when the engine is warm. I usually run on premium fuel, so I don't think it's a fuel grade issue. You mentioned the knock sensor, is it possible for it to cause all these symptoms, including the smoke?

While a faulty knock sensor wouldn't directly cause smoke, it can definitely mess with the engine timing and fuel mixture, potentially leading to incomplete combustion, which could explain the smoke. However, with all the symptoms you're describing, especially the knocking and smoke, deposits in the combustion chamber causing pre-ignition or even piston slap seems like a very likely culprit. Running a compression test would tell you more. At this point, I'd suggest getting it looked at by a workshop that can scope the cylinders. Running it too long like this could cause damage to the cylinder heads.

I appreciate the insight. I'll get it to a workshop. Turns out it was, as suspected, deposits in the combustion chamber. They cleaned the combustion chamber and the intake valves, reset the error codes and the car runs very smoothly now. It set me back 425€, but it seems that the issue has been resolved.