1990 Volvo 760 4 cyl. Turbo. Drove the car to work, everything fine. Got off work, car wouldn’t start. Cranked but wouldn’t start. It was getting spark. Changed the fuel filter, it ran perfect for a month.
Drove it to town a month later, shut it off, then trying to start it, would crank and crank eventually start but run real rough. We got it home…barely.
Replaced the fuel filter again. Still wouldn’t run right.
Replaced the fuel pressure regulator. Same problem.
Replaced the throttle positioning switch. Same problem.
Replaced the air control valve. same problem.
Found out that this car has an on board diagnostic doo hickey. Found out how to check each sensor and component individually. All sensors and components are working.
Checked both fuel pumps and they are working.
If I unplug the air flow sensor and the air control valve sensor, I can start the car using starter fluid and it will idle all day with out missing a lick.If I plug in either one of the sensors, it will kill it immediately.
I don’t know what else to do to make this machine run.
Do you have any ideas.
Did you try and clean the MAF sensor? There’s a special aerosol spray you can buy to clean it with (use the right stuff). I’m not sure what the “air control valve sensor” is, unless you’re talking about the idle air control, which can also be cleaned with the correct aerosol.
Out of curiosity, how much did you spend so far?
Edit: Does this car really have 2 fuel pumps? I know some vehicles do, but most of those also have dual tanks.
Chase
My '74 Volvo did have 2 fuel pumps, and it only had one tank.
It also had more mechanical issues than all of the other cars I have ever owned, put together!
My Volvos also had two pumps, one in the tank to prime the pressure for the main pump.
Cool. I’ve really only seen them on Jag’s (dual tanks, fuel pumps in the trunk), dual tank pickups and the like.
Live and learn. Thanks. 
Chase