Weird thing: Our '84 300DT is running fine now (after I put approx. $1500 in parts and weeks of work in it...) except for one thing: I have strange vibrations, occuring exactly between 1600rpm and 1700rpm, no matter if I'm driving or standing (-> engine, not drive train). I asked several people, most tend to the conclusion the IP must be bad (insufficient fuel delivery to one cyl. at exactly this rpm., leading to rough idling ). I'm just trying to save another $1000 for a new IP, any thoughts?

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