Okay so, I own a 1991 240 wagon and I’ve had this persisting issue for quite a while. Whenever I drive for more than about 15 to 20 minutes, the acceleration starts to hesitate a bit before it then starts to have a diminishing performance（ it jerks forward when I press down on the pedal and goes very slow) then the vehicle shuts down all together. If I wait a bit and crank the ignition, the vehicle will start and will be fine for another 15 minutes before doing the exact same thing as before. I haven’t the slightest clue what the issue could be. I’ve replaced the ignition wires, spark plugs, i got a new throttle position sensor, I replaced the crank shaft position sensor, new fuel pump relay, new fuses, cleaned the throttle body, new fuel filter and some other stuff that I fail to recall at the moment. All that and the problem still persists. I’m at wits end and was hoping someone would be able to assist me with this issue. Any tips at all is appreciated.

 

Have you checked fuel pressure? With worn out pumps (2) the pressure can drop after the pumps have run for a while (when they are worn out).

Or - your fuel system/fuel pump relay (white relay under the dash on the right side ) may have cracked solder joints (common) and after it heats up after running for a while - the poor connections heat up and prevent the fuel pumps from working. Also make sure the 25 amp fuse under the hood has good connections.

 

This site has a nice description on how to check out you fuel pumps:

In the Tank - 240 Volvo Tank Pump and Sender