Volvo: fuel filter or ?, fuel pressure regulator, fuel gauge

Question
Volvo 88 244 DL-- Seem to have problem when running with not getting fuel.  Gauge seems to go up and down, and car has rough idle.  Changed fuel filter, but problem still exist.  

Answer
Clint,
Make sure the feed pump in the tank is working. What is the fuel pressure above 40psi? If yes then that is ok. Any lower that is not enough pressure. That could mean the fuel pressure regulator is bad or feed line is blocked. What is the cars running history? Perhaps the injectors are blocked and need cleaning.