My 86 240 suddenly started idling really rough (warm or cold) and putting out horribly smelly exhaust. Plugs are sooty black. Mechanic had the car for 3 days and charged $200 without coming up with a diagnosis. I decided not to pay him any more and learn about the fuel system (which I have always shyed away from before) and start looking for the problem myself. Tested all connections at the LH 2.2 control unit (according to Bentley) and found no continuity at the no. 12 terminal to the throttle switch when the throttle is wide open. Could this be the cause of the problem? Resistance at AMM checks out OK, coolant temp sensor and O2 sensor supposedly were checked out by the mechanic. Do I need to take apart the throttle assembly and clean it or simply try to adjust the throttle switch? How will I know if the switch itself is faulty or just not adjusted right? Am I even on the right track, or can a maladjusted throttle switch alone not cause all this trouble? thanks, Karin