10 days ago I drove 500 miles to Denver and dropped the car off at a MB dealer for a new harness. I paid about $500 for labor, and MBUSA and my original dealer split the part cost. One worry out of the way.
But the car still ran rough. I basically flipped a coin as to whether to leave it at the dealer for another day or take the car to an independent tech with a good reputation, and the independent won the toss. After 3 hours (at $85/hr) he discovered I had a bad coil. I had tried to check it with an ohmmeter but somehow fooled myself. I had gotten good readings by pressing the ohm-meter probes hard against the coil. Apparently the internal connections were erratic. At the time I thought the ohm-meter probes were not sufficiently extended out of their spring-loaded insulators. (Time for a new meter.)
The bad coil had blue-grey stains on its case--maybe from internal arcing. As recall, the other two coils also have these stains, although not as bad. In retrospect I should have bought a spare coil when I replaced the spark plugs, ignition wires and coil-connector boots. (The labor charge savings would have paid for a lifetime supply of coils.)
Thanks again to everyone for your help.
94 E320 Wagon, 170k, totalled in 2006
2002 BMW 525i Wagon, 75k
1991 BMW 318is (two of 'em)