I don't know, I am targeting it because its the only thing left. I would assume that injection pump problems are going to be noticeable at low RPM just like a bad injector due to the low injection volumes and lower kinetic energy at the flywheel. Fundamentally they are all combustion related events that exhibit themselves as a vibration. These can be related to the following:
Compression
Injector spray pattern
pre-chamber problems (loss of ball)
delivery valve sticking/ improper seating
improper valve lash
Injection pump malfunction (wear/misadjustment)
Feel free to add to the list, I'm just listing the most obvious to me.
I am sorry to hear about your vibration, but at the same time I'm glad to hear that I am not the only one with these symptoms.

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