I had the same/similar problem. It was pretty much most of the fuel-related electronics (i.e. relay) and the fuel pump check valve (cheaper than it sounds). Took the Volvo dealer 4 months (intermittently) and about $4000 to figure and fix everything, but 9 months later it's doing fine (knock on wood!). Use the onboard diagnostic system and get the Haynes (I think mine's the Haynes) manual for the 1990 cars, it lists what each means without having to look it up on the computer. As old as the car is, it's worth checking all the relays and such anyway. Good luck!