Volvo: stalling out, fuel pressure gauge, driving watch

Question
I've had my 1990 Volvo DL in the shop 4 or 5 times because it stalls out while I'm driving every so often -- for no apparent reason.  They've replaced two parts, but it hasn't improved the situation.  It'll run fine for a few days, then stall out again -- twice in the middle of the freeway.  Any ideas?

Thanks.

Answer
Bev,
Well you need to see what signal is missing. Put a fuel pressure gauge on the car and while driving watch to see if when it stalls you are losing the fuel. If the pressure stays up and there are no faults posted I would say the power stage for the ignition system. Have you taken the vehicle in for regular repairs? Things like the fuel filter, air filter, throttle housing all been replaced cleaned and adjusted?