I have a Volvo that had symptoms like this (progressively worse):

1. Stumbled only when starting out in 1st gear.
2. Stalled at a stoplight and would not restart
3. After cooling off, restarted and drove (BADLY) home. Intermittent loss of power, surging. Sometimes cut off when idling..always restarted. Replaced Air Mass Sensor to no effect.
4. Replaced spark plugs/wires. Ran perfectly for a couple of days.
5. Then, began to intermittently lose power. At idle, would sometimes rev up briefly for no reason. Sometimes quit running at idle...always restarted.
6. On a 25 mile one way trip. Ran intermittently poorly. Twice just cut off as if the ignition had been cut. Restarted immediately. Felt as if I had to nurse it up to speed....little low end power. Ran better at high speeds.
7. Car shut off as a stoplight was approached. Would not restart...had it towed.
8. Found arcing rotor. This is a Chrysler-style distributor with the timing blocks attached to the rotor. Arced through the rotor to the distributor shaft.
9. replaced rotor. Car starts, but all prior symptoms are still there.
10. Testing showed intermittent voltage rise on injectors while idling, causing the car to speed up and sometimes run rich. Suspected a computer (bad choice...not the problem). Replaced computer...same symptoms.
11. Drove car around the block. It shut off and would not restart. For the first time ever, I got no spark out of the coil. It restarted after it cooled off.
12. Ordered BOSCH style replacement distributor from '84. Got a new plug with it and wired the new plug into my existing ignition wiring. 2 of the wire colors were the same (yellow/green). One was not: red/black. I wired it anyway.

The car now runs perfectly and I have a ton of perfectly fine replacement parts for this car. The problem was the sensor in the Chrysler-style distributor.

What a ride. Thanks for the hints on this board. Suggestions were good and I think SOMEONE early on suggested the distributor sensor.