Greetings,
I just took ownership of a nice, well cared for 300SD w/OM617a. I picked the car up after several viewings and discussions with the owner. It ran fine and performed very well on the 3 hour drive home on the interstate. The next day when I started it (cold) I noticed a bit of what i believe was injector nailing when the engine was heating up.
I adjusted the valve lash (several were very tight out of spec), did a diesel purge, and replaced both fuel filters. As another item, I blocked the EGR vacuum line.
Now, the engine starts and runs beautifully...except for a nailing/tapping noise now at 1500-1800 rpm while accelerating LIGHTLY. If I give it more pedal, the noise immediately dissipates. Regardless of load, it never happens above 2k rpm.
I thought..crap, I made it worse. I checked my valve lash again. All good. Went for a drive, same symptom. I removed the BB from the EGR vac line, this made it much better somehow, but the nailing is still there intermittently when accelerating lightly or cruising slowly. Other than the noise, the engine runs excellent. Plenty of power, smooth idle, hardly any smoke, etc.

Any suggestions of how to proceed with troubleshooting?

A friend says that these engines like to be run hard and I should troubleshoot with a little cetane booster and a heavier foot, but I'm not sure I buy into that yet...

Thanks in advance,
Matt