I'm the guy with the car in New Mexico. I had the car in a shop for three days with similar symptoms: cold start OK, accelleration, normal running OK,
all fuel leaks cured, new filter, prefilter, clean diesel, no codes, good engine mounts new tensioner, belt, idler wheel, tensioner shock, new alternator,good glow plugs, everything working on car, good battery--still runs rough when at operating temp and only when in neutral or park. Shift into drive or reverse and it idles smoothly. Shop said POSSIBLE ECM problem but no way to tell ie. start throwing parts at it. The car was running well overall so I've been driving it until yesterday when all of a sudden it died at cruise with apparent fuel starvation. I pulled over, turned off the key, waited
five minutes and presto--restart and running as normal for ten miles. The same thing happened again five times until it limped into the airport parking lot where it now sits. Finally the CEL came on, so we finally have something to work with.
All of this started last month with leaking o-rings on the injector pump and has really stumped everyone. I called the local MB dealer and asked the parts manager how many ECMs and injection pumps they have sold for these cars
and the answer was 0, so he thought it was unlikely to be either of these two items especially due to the intermittent occurrence.
We shall know more later since I'm taking it to yet another shop today.

Steve

not very impressed with the repairability of this model