I also do not know where the problem is. Elimination of things does help usually. Clearing the engine is fast, cheap and easy. Clearing the fuel system is longer. With his description I would clear or condem the engine first. Only takes a minute or two once you are familiar. We have to start making use of tools and systems that are cheap, easy to use by the average member and pretty conclusive as well as fast. Even if it is not the engine this time he will never forget how to check it in the future. Next time it may nail it for him. It is just a tool to try to avoid high garage charges and increase our abilities. I originally got into this as there were too many times people complained about rough idles. The usual approach was to spend money and keep spending. In otherwords they were guessing. We needed better and it is my belief this is one way. The best thing about reading milli volts is it makes you think.

Ok, so this car usually runs on Veggie supreme. But lately two of my oil sources dried up. So I was without oil. Over the weekend I apprehended some oil and was driving the car, which continued to idle roughly. Once I switched it to oil it began to run as normal. MORE POWER, SMOOOTH IDLE, NO SMOKE... My WVO system is independent of the diesel system. So minus the diesel tank, and fuel lines the motor is running fine. So, as some have suggested it must/may be the tank strainer. So I will probably try that this weekend. I am somewhat/highly relieved!!! I will keep givning updates. Thanks for your help.

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1982 300CD (Veggie)
1975 240D
1986 190D (lost a bearing)
1982 240D (dead eng.)

Have you checked the primer pump?