Volvo: 1995 volvo 940, fuel pressure gauge, 1995 volvo 940

Question
I have a 1995 Volvo 940 that sometimes stalls out, usually in wet weather. My Volvo dealership told me the problem was fixed after spending some money on it last year but it is definitely not. I have made a 3 hour trip in the rain without it stalling but a few weeks ago while driving 2 hours home from school in the rain it stalled out on the turnpike. The RPM's will begin to drop and when the gas pedal is pushed they severely drop until the car eventually shuts off. After waiting a while it will sometimes start up but not always. It is very unpredictable, sometimes it has no problems in the rain and sometimes it won't come close to starting it will just make the start up noise. I have a product called "wire dryer" which is sprayed under the hood and seemed to work for a while but not so well anymore. It worked for me on the turnpike but then the car stalled out again 5 miles later. I had it towed home and, while still raining, it started up in my driveway. It rained the whole next day and would not start, so i gave it a day to dry out in the garage and it started up. I had a few ideas on what was wrong, but its so random when it happens that I cannot trace it back to one specific condition. What could this problem be?

Answer
Phil,
As you stated the problem is intermittant. When I get these cars I put a fuel pressure gauge on and drive carring some spare parts, like MAF fuel punp relay, power stage, injection relay, flywheel pick up, coil. I drive until the fault happens (if that is possible) and then read any fault codes and if I have a loss of fuel pressure when the fault happens, go to the pump or relay. If only the tack falls then the power stage or coil. If it just dies without the tack falling or loss of fuel, then the injection relay.