I also would suggest adjusting valves and checking and replacing chain (if needed) as a good place to start. But I also would urge anyone who suspects they have an injector "nailing"(injecting fuel too early) to not drive another mile until they have had their injectors checked/repaired. I've seen the inside of an engine(240D) that I'm pretty sure had this problem and it was ugly! Broken piston and multiple cracks in the head in one cylinder. I have the injectors out of a 300D, at the moment , for this very reason.

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Diesel-guy