My problem is solved too!!! (with crossed fingers and knocking feverishly on the nearest chunk of wood)
I don't want to jinx myself, but the rough idle at normal operating temperature appears to have been linked to one of the two minor updates that I just completed on my 1991 560 SEL:
new bosch spark plugs
new voltage regulator
The plugs were fouled with black carbon deposits, although the one closest to the driver (I don't know how they are numbered) had so much buildup that there was no gap, just gunk! The interesting thing here is that the car did not miss all the time. If the problem were just a fouled spark plug, then it seems like the car should have run badly all the time, as the condition of the spark plug firing end is not as dynamic as the temperature of the car. Can spark plugs lose their functionality as temperature goes up?
The old voltage regulator was VERY worn, with less than a centimeter and a centimeter and a half left on the brushes. I don' know how much that part is related directly to the miss problem, but I have seen in other posts that a voltage regulator ($17.95) can take care of problems such as:
rough idle once the car reaches normal operating temperature
a major nuisance (sp?)
SOOOO, I know that a car with 260k is likely to have other issues, and I have read here that the oxygen sensor, ignition coil, plug wires/ends, idle control valve, and fuel injectors are also prone to problems similar to those I just described. Are there any recommendations about which of those parts to replace and in what order, if I were to put about a hundred bucks a month into the car?I hate to just drive it and wait for things to break.