[NCRUZ]

I have owned my 1991 300D for over a decade now. I have driven this car through the continental US except for the North Western part of the nation. Im in an overseas assignament now an brought the car over with me. Recently the rpm`s quit reading suddenly and the a/c clutch stops working while driving. The rpm`s raise up and lower under 500 when shifted into gear. I did some troubleshooting with the wiring; changed the prm sensor with no effect, there is no engine management (unplugging the EDS has no effect on the engine status while the simptom is active) I havent been able to locate the power souce for the EDS. The car still drives otherwise ok and gives aroun 28-30 mpg. I still have no clue of whats the cause; but everything might work ok today and not tomorrow and also intermitten while driving. Can anyone offer some insight before I subcome to take into the dealership?