M Klasse diesel cylinder pressure fluctuations

That sounds frustrating. I've got an M Klasse too, though I can't remember the exact year right now, and I had a similar set of symptoms a while back. Reduced power, check engine light, the whole shebang. For me, it turned out to be a cascading error. One little sensor went bad, and it threw off a bunch of other readings, making it seem like I had all sorts of problems. Have you had the codes read? Knowing the specific error codes will point you in the right direction. It could be anything from a faulty sensor to a vacuum leak affecting the turbocharger or even something fuel-related.

That's actually really helpful. I did get the codes read, but honestly, there were so many, it looked like alphabet soup. The mechanic mentioned something about cylinder pressure imbalance, but also threw around terms like 'potential fuel injector issue' and 'possible intake leak.' Any chance you remember which sensor went bad in your case? It might give me a starting point. Is there any simple way to check for a vacuum leak before diving into the complicated stuff?

I wish I could remember the exact sensor, but it was a while ago. Honestly, with that many codes and the cylinder pressure issue, I'd really recommend taking it to a trusted mechanic. A vacuum leak can sometimes be found by listening for a hissing sound, but honestly, with modern cars and all the hoses running everywhere, it's tough to pinpoint without proper equipment. My issue ended up being a relatively cheap fix once they found the root cause, but chasing all the individual symptoms would have cost me a fortune. The fact that the issue is consequential could save you some money, if you are able to identify the initial problem.

You were spot on! Took it to another mechanic, and it turned out to be a faulty sensor, just like you said. It was throwing off all sorts of readings. They replaced the sensor, cleared the codes, and it's running like a champ again. The cylinder pressure fluctuation was a ghost error all along. Best part? The repair cost was basically nothing! Thanks a ton for the advice; you saved me a ton of stress and probably a lot of money!