This may not be very helpful, but I can tell you of something that I encountered back in the late 1980's: I would occasionally run into a vehicle which would run on for some time after the key was turned off (not dieseling, but actual ignition). What I found was that the cooling fan, which was running when the car was turned off, would continue to spin, acting as a generator and backfeeding power to the ignition system, letting the vehicle run. Disconnecting the fan killed the engine. Apparently there was a diode somewhere in the fan motor or in the harness that was meant to prevent this, and failure of this component allowed the reverse flow of power. My solution was to solder in an appropriate diode, and the problem immediately went away.
Our Saabs may have a more sophisticated problem than this, but the easy check would be to disconnect the fan, leaving everything else hooked up, and see if the problem is "cured."