1983 380SL will sometimes (not always) throw a LOT of dark smoke once I've driven about 2 minutes down the road after a cold start. It only lasts about 30 seconds to a minute (I said a LOT of smoke--James Bond smoke screen) then no smoke at all! It never happens if the motor is already warm. The car has just over 100,000 miles, is well maintained, and always makes good power. Any ideas?