Just a possibility....

Change the rubber fuel hose that connects the metal fuel line from the tank to the plastic in-line filter. I wont go into boring details, but I recently had a week long fiasco that ended up costing me $500, and the problem ultimately was fixed by replacing this hose. My car behaved as you describe, and it was due to this line which was hardened (probably original) with cracks in the rubber where it connects to the inline filter. When I clamped it onto the filter, it distorted the cracks, allowing air to enter.

Get regular Goodyear black braided fuel line at your local auto zone.

There are many other causes of the symptoms you describe:

- Clogged fuel filters, clogged tank screen, algae in tank - sounds like you have some crud in the inline filter..

- adjust valves...valves typically get tight over time...this prevents valves from closing causing you to lose compression, noticed especially under load.

- bad injector(s) -take them to a shop where they can test spray pattern and release pressure. Clean out where the injectors screw in and seat, and install new heat shield washers.

- air in fuel lines - make sure all connections of the hard fuel lines from IP to injectors are tight. Check entire length of hard fuel lines back to the tank for leaks. While you are replacing the rubber hose (above), check and/or replace the two rubber lines that connect the hard deliver & return lines to the tank

- clogged delivery valves - these are located on the injection pump, and the "spider" fuel lines connect directly to them. Inside there is a spring, and a little moving metal piece which must slide freely inside the housing. Remove them, clean, reassemble, and replace the copper crush washers. IMPORTANT...do not remove the apparatus held in place with two nuts (one for each fuel line where it connects to the IP)...the delivery valves are on top of these and just unscrew.

These are just a few things...there may be other causes related to vacuum, egr, banjo bolt & line on intake manifold, etc..

good luck,

Mark

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)