Actually Larry, I wasn't thinking of a jammed chain, but a faulty timer. I think the injection timer acts to advance the injection timing as engine RPM increases. I've never had one apart, but from the manual it appears to be a "centrifugal advance" mechanism built into the sprocket that drives the pump. I know it is a reach, but when Steve mentioned timing it made me think. I've always wondered if the timers wear and if that could explain the erratic nature of the idle on my 1983 240D. I've checked everything. One day it idles like a gas car, the next day I shakes so much you would think it's going to tear itself out of it's mounts. It's going to be interesting to see what you find. Good luck!!