If this is a pre-1989 car, I'd expect a bad distributor. The hall sensor on all of these will eventually fail and short out against the dist backing plate.
If it's 1989-up, I'd expect the same sort of failure from the crank sensor (rpm sensor, impulse sensor, whatever). Wires fatigue and fail. Can be intermittent.
Either of these things could do it in a car of this age.
And it would help to identify the year, engine, and possibly transmission, in follow-on posts... significant differences apply to the 88/89 model year divide, as well as Turbo vs. non cars.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 229K, 88 744GLE- 218K, 82 245T-181K Also responsible for the care and feeding of: 88 745GLE, 231K, 87 244DL, 239K, 88 245DL, 246K