Ihad a new car in 1995 come in with a bad crankshaft sensor. It was mechanicaly perfect, and the computer checked out fine, but it would backfire through the intake 40% of ignition events, and usualy stalled within a minute. I think crank/cam sending errors are among the harder ones for the computer to detect, and you may have an intermittent problem. Still, I would test the sensor before buying a new one.