hi, if its smoking from the exhaust its probably gone onto safe mode, my van did this and it was the injectors gone faulty, the only way to find the fault and reset was to have it pluged into the merc computer to diagnose.(my local garage had merc softwear to diagnose this. not a merc delearship.)
one other thing to check first if not smoking is the tiny glass blob sensor in the air intake pipe to the left of the engine , the pipe that feeds air to the aluminium manifold, just to the left of the oil filler cap you will see 2 wires going to the sensor in the rubber pipe, remove the sensor and clean with meths, when cleaned it takes a few miles for it to start working again. its the tiny glass blob that gets contaminated with oil, my old van did this about every 6 months.
cliff, November 2009
