SDK,
The idle settings should only be adjusted after everything else is working correctly, including ignition system. If the idle mixture is set too rich, the car will idle rich when it's warmed up. Suspect other things first, like a leaking CSV or injector as mentioned by Rodd. There may be other possibilities if these aren't the problem.
The CSV should have a small 7 or 8 mm hex screw in the side. If so, you can check for CSV leakage by removing this screw, then put a rag below it and drape another rag over the CSV to catch fuel in case it leaks a lot. Turn on the ignition so the fuel pump runs, then check the screw hole. If fuel is dripping, dribbling, spraying out, the CSV is leaking. The factory spec is no more than 3 drops in 60 seconds. New CSVs are expensive, but many owners have successfully repaired them themselves for next to nothing.
Fuel injectors are probably best checked off the car with proper test equipment, which I understand is rare, but a diesel or injector shop can get close. I imagine there are DIY ways to check leakage on the car as well, if you're so inclined.
Good luck!
George Davis
'69 280 SL Euro manual
