Working through exactly this kind of thing - with similar symptoms. Guys here have been very helpful...

Mine was a fuel starvation issue. Old diesel fuel/sitting for a couple of months in 30+ yr-old lines, which deserve replacement anyway... Well, you do the math!

Replacing both fuel filters has been a day and night fix, even if only a stopgap. Next steps are tank cleaning, replacement of lines, etc.

If you're burning VegOil, got a feeling you have a slew of additional variables. Experts here can help.

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'83 300 SD
'05 E320 4Matic
'06 BMW 530 xi
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr