Engine stalling/stumbling problems can be caused by a failing mass air flow sensor.
Car Problem Reports
Volvo 940 Engine Stalling Due to Mass Air Flow Sensor Failure
Volvo 940 Problem
Engine Affected: 2.3L 4 Cylinder
Visitor, 1992 Volvo 940, 2.3L 4 Cylinder, 125,000 mi
Engine stalling/stumbling ( jumping like a wild maverick horse ),
was discovered due to a burnt relay gas pump, then the gas pump was measured OK via pressure meter. So, the car ran with very low power in the first few gears with the weak gas pump. One day i said let me change the gas pump just in case, and BINGO ! The car power came to life like when it was new !
This car is so good that ran with a defective gas pump !
Lucky it did not leave in a risky lonely road !