Your engine needs clean fuel!
Clogged fuel filters can cause a lot of running issues below:
- Idle issues
- Hard starts
- Loss of power especially under load
- Harder working fuel pump

This fuel filter is probably close to original on this low mileage 25 year old E34 525i.
Your fuel filter is a wear item and should be replaced at intervals recommended by the manufacturer. If you are unsure when the last time yours was replaced, it may be time to keep your engine running well.