Hello everyone...Having recently driven my 1985 500sel from SF to Pittsburgh, the only problem being a need to replace the Catalytic Converter in Colorado, we've developed a mysterious symptom. Somewhat abruptly, the engine has developed a slight put-put sound, and the initial RPM when starting the engine are very low. The RPM gain momentum to normal, the engine doesn't die. When shifting from D to N the revs increase to 1100r then settle back. The car has had recent plugs, wires, Distributor cap, air cleaner and fuel treatment....any ideas? Thanks, Ken Heimbuch, now of Pittsburgh.