My '89 525i has has fuel issues since i've had her. Right now it's sitting in my driveway not going anywhere. I kinda need help, too, but i'll tell you what i have done so far to try and fix it.
1) Replaced fuel pressure regulator 3x - Use only BMW part. No one else sells anything that works well (PEP BOYS, Western Auto, Advance, Auto Zone). Fuel pump in gas tank was OVER pumping and blew out the regulators i replaced which led to an over fueling problem which made it hard to start. If i shut off engine before completely warming up it would not start back up until at least fifteen minutes later.
2) One technician installed a fuel pressure regulator for a 7 series which ofcourse did not work.
3) Car is worse than ever now. She runs like i have water in the fuel, but it isn't water. Seems like it's running on half the cylinders (when it runs).
I hope something in here helps you find your issue, maybe something you havent thought of yet, but I would be interested in knowing what you end up doing to fix yours. The three different techs who worked on mine are stumped as well, but they still keep charging me for doing nothing.
SIX of all this BS