Another solution to the list
Glad to hear that you solved your problem with the idle control valve. Did you happen to pull the Bosch plugs after running them for a hundred or so miles before changing out the idle control valve? Just curious to see if they would be black as well indicating either an over fueling problem or under aspirated which was your case. My plugs actually looked pretty darn clean after 11,000 miles with the exception of number one and six plugs which seemed to be tanted with a light brown instead of the usual grey deposits on the electrode ground. These were also the two cylinders least affected when pulling the wires off the plugs. Could be just a coincidence but the spark seemed hotter on all the rest when removed. I also noticed two spots inside the distributor cap on two cylinders that were more arched then the others, but didn't notate which cylinders they were. I think my problem may be solved with this new cap I purchased. I'll find out as soon as I get the lower cap cover as it shattered upon removal.
Glad to hear you're up and running, another success story. I do have to say that after cleaning up the inside corrosion of the OVP, that the car starts easy again and it even idles 200% better than it did. Don't know what it has in common with the idle but it worked.
"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