This wonderful experience occurs with my 83 Volvo 245. I can see bubbles in the clear hose from the filter. The filter is full when I remove it. I have replaced the filter also. Has no wet spots anywhere from the tank to the filter. Dropped the tank, and the pickup is clear. I have replaced the feed hose to the filter. Pump is not leaking. Stumped.
A vacuum gauge on the fuel line will tell you if the pump is pulling hard and bring air out of suspension.
A full filter can be a sign it was clogged.
Air will often stay in a clean fuel filter, because it has a hard time pulling through the diesel-soaked paper.
The filter was only a couple of months old. I will drive some today and see what happens.
Replaced filter housing with one from an MK1 Jetta. Problem solved 180 miles so far.
I had a similar problem once with mine, after searching long and hard I found out it was the plastic fuel heater fitting on top of the fuel filter. Installed a o-ring and problem solved. That fitting is only held in place with a spring clip and I guess it wasn't exerting enough pressure on the fitting to seal the hole - hence sucking air. The older filters don't have the fuel heater.
Still running like a scalded slug, but thats a good thing.