I would appreciate suggestions as to next diagnostic steps with which to pinpoint a problem I am having with intermittent rough engine operation on my 1983 240D with manual transmission (204K miles).

Most of the time it runs fine with its typical nice muffled diesel engine sound and smooth performance. However, about 15% of the time, it will idle and run rough and louder from initial starting and will continue that way, with poorer performance, throughout the entire time the engine is operating until it is shut down. I have observed that a change of state, i.el from good to bad or the reverse, never occurs during the time the engine is operating and also that once the condition occurs during a start and operation, it is likely to exhibit the same condition during subsequent starts and operations during that day. The next days initial start is most likely OK (~85%). I have verified that the intake manifold butterfly valve is operating smoothly and is not sticking closed or open. All of the mechanical throttle/injector linkage seems to be operating freely. Does the intermittent occurrrence and the nature of the problem suggest a vacuum issue -- pump, valve, lines, etc.?

Thanks

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Okiebenz

First change fuel filters. Sounds like a possible fuel flow prob. Start with filters and work back to tank (lines, tank screen).

Thanks for the response. I changed both the fuel filter and pre-filter recently and I have not noticed any lack of flow at the pre-filter. I am fairly new to this forum and I believe I may have posted the original message to the wrong area. I will also post it in the Tech Help area.

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Okiebenz

Have you tried massive dumps of Redline or Stanadyne or some such in the fuel tank? Algae or other gunk in the fuel system could be the prob. Consider diagnosing the tank to filters before moving into the Injection Pump.