This is in reference to my posting on sluggish start from standstill:
Turns out the air purge pump handle was not screwed back down all the way and was causing a slow air leak into the system as well as loss of fuel through slow dripping.
I am suspecting the new mechanic who took the place of the beloved and recently retired (and very missed) diesel God at the local MB dealer. The car was in the shop several months ago for the A/C system refurbishing (works great) and they had taken it upon themselves to go ahead and replace the fuel filters, which was fine with me. My guess is the air had to be manually pumped out afterwards but the handle was not fully locked down. This afternoon, after noticing some wetness around the prefilter and bleed pump assembly I discovered the pump handle was loose by about 4-5 turns. Not likely this thing would loosen itself by that many turns. This was probably causing the air leak into the system. The owner's manual says the air is bled automatically so I'm guessing there was seesawing going on with the leak and then the automatic purging.
After tightening down the handle, the rocking idle is completely gone and also the sluggish start from standstill. The car also feel more peppy all around with much better throttle response and best of all seems to be more agressive and confident at highway speeds.
I am a happy puppy now.
By the way, I did remove the banjo bolt from the intake manifold and cleaned it. Although there was no air blockage, there was buildup of tar-like substance and it was cleaned up.
Thanks to Alain, Nicolas and TXBill for this tip. While taking care of this chore is when I stumbled upon the leaking purge pump handle.
And TXBill, the tach needle is still registering fine with the "cigarette butt" trick.