I should add two additional things:
Is it possible I may also be running a bit lean?
In the past month or two I have noticed the engine stumbling after the first startup of the day. It was as if it was starved of fuel; you floor the pedal and nothing it would rev right away; only after a second or three would it rev normally. Once it got warm, or if I revved it at 2000 rpm for 30 to 60 seconds before driving, the stumbling would not happen. This morning was the first time that did not happen, which seems to suggest an electrical issue.
Also, duruing the past couple of months, the plug wire case had been very loose, but generally remained on top of the engine.
Is it reasonable to assume that after weeks of driving with dangling plug wires that one or more of them came loose at the distributor and, as we have seen, the ignition coil?
2001 E430 4matic
Gone but not Forgotten:
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black