You hadn't mentioned before that you were a mechanic shop owner before, great to here from some folks out there with expertise in the field. Do you do general mechanics of specialize in Benz or foreign auto's? If I can find a day off, or get the days stretched a little longer I'll pull the plugs after the rough idle as you suggest. At present I'm seeing dark going to and coming home from work so it will probably be several days before one comes available that I can get free. Have you seen any other instances where the idle on the car became rough such as a Benz, where it wasn't the injectors or fuel or vacuum related?
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan