It could be a bad ignition control module(ICM), but I can't remember how to test it. On the 91's the crankshaft position sensor signal goes through the ICM before it goes to the ECM. The ECM uses the crankshaft signal for ignition timing. You might want to get under the car and find a wire harness that runs from the front side of the motor(ICM to be exact, the coils are mounted to it) under the oil pan and to the crankshaft position sensor to see if the harness is in good shape(not cracked up, worn through or otherwise compromised). You may want to check the other wires at the ICM to make sure they are not backed out of their connectors