We just had a '94 850 in our shop with the exact same code but it was a no start. It turned out that the main relay wires at that relay were in bad condition, not making contact. That's the large relay that sits in the panel just above the radiator on the left (drivers) side of the car.
Bad ECUs are highly rare SO before buying another, either inspect the wiring in that area (remove relay to be sure) or even try another relay as apparently that will cause a "no spark" and a false RPM sensor fault code.