could be the pnp switch try ratcheting the shifter back and forth many times real fast if that works then it may be the pnp volvo speed bay 13 has a good thread for this

did you replace the relay switch? located under the fuse box, read the engine stall thread seem's the switch is a high percentage of the problem
just replaced mine yesterday after having stall/start issues instant fix

Replaced evaporator on my 94 850, I re-posted the picture thread (good for a year) very helpfull make sure you loosen the heater hose coupler through the fire wall otherwise you may crack it like I did ($50) when you pull the white housing away from the fire wall .also loosen the hex nut on the smal...