I had this exact same problem a few months ago. I installed a spare Fuel Pump Check Valve that I had, and no more stalling or hard starting issues. Once I had a large enough order, I bought a new one from FCP. I installed the new one and kept the old one as a back up. Art Benstein said that the spring in the check valve tends to corrode with age.

http://www.fcpgroton.com/productexec/product_id/5147/nm/Volvo_240_Fuel_Pump_Check_Valve_1985_1993_Bosch_/category_id/149
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If it needs to be maintained, repaired or replaced on a 1990 240, I've probably done it. '90 240DL, 297.9K looking forward to 300K badge (or sticker??). >>You haven't really worked on a car until you draw blood<< :-}