A lot of the idling racket on these engines originates in the stone-age vacuum pump even when operating normally.

If the clacking sounds like it may be from a single cylinder, you may be able to isolate it by one of two methods. I found a mechanic's stethoscope useful for locating noise sources. As a definitive test, barely loosen the injector hard line nuts one at a time to see if the noise stops on that cylinder. It is like pulling a plug wire on a gasser.

I agree with another valve adjustment after a few thousand miles. You may find that it gets quieter after driving it for a while. If the noise source is in the valve train, it takes a little while for the parts to get used to their new relationship after an adjustment.

A QUIET OM616/617 IS ONE THAT NEEDS A VALVE ADJUSTMENT.

idling racket
 

Ok Rocky. thanks for the "tips"! Have to agree with your assessment about the "stone-age" vacuum pump. That pump is ALWAYS on my mind, weighing quite heavily. Wondering if it's gonna explode and when....if the result will destroy my engine...should I buy a "new" one....try to rebuild the one I have, and on and on and on. Realizing rebuild kits are now NLA, I guess the best we can hope for is bearing replacement?
This has to be the "weakest link" in the chain on these cars. Don't know what the engineers were thinking when they decided to go this route. They could have, at least, protected the rest of the engine, somehow, when these things "grenaded".
I'd be very interested to hear from other members about their vacuum pump failure experiences.
Here's an EXCELLENT write-up/how to, from member "Stretch", about the dread vacuum pump. Many large, clear pics and great explanations along the way. If you've never seen any of his "how to's", you're in for a treat. He does excellent work, is extremely knowledgeable and thorough and the end result is always quite impressive.
http://www.peachparts.com/shopforum/diesel-discussion/339870-more-than-you-likely-ever-want-know-about-om61x-piston-vacuum-pumps.html