Mercedes-Benz W210 OM606 diesel shakes at warm idle

The symptom is well known on the OM606, and it is usually felt in the 600–800 rpm range. The cause varies: often it is the injection pump delivery valves, worn injectors, fuel leaks or the pump timing. The fault should be looked for among these one at a time.

The delivery valve cuts off injection at the right moment so that no after-dripping occurs. When the valves are worn, the engine shakes when warm. The O-rings and copper seals are usually replaced at the same time. The pump's injection timing should be checked during the work.

The condition of an injector is determined by its opening pressure and spray pattern; measuring the leak-off alone is not enough. A rattling injector is found by loosening the injector lines one at a time with the engine running: when the noise stops, that injector is the faulty one. Also check the overflow hoses and the O-rings and quick connectors of the fuel lines.

A dirty mass air flow sensor can make the engine run roughly and smoke. Cleaning it with a cleaner meant for electrical parts has helped. If the sensor's hot wire is gone, the sensor must be replaced.