1991 E-150 idles good, but keeps stalling in gear

It is a 5.0 V-8 with aprox 160k miles. Vehicle starts up fine and will idle fine. Put in "D" and about a mile later the engine will stall when trying to accelerate after coming to a stop. Engine will be hard to restart, then, while in park, if accelerator is depressed to the floor, heavy, black smoke will be emitted. The engine will remain idling and the vehicle can be driven, for a short period. Acceleration must be very gingerly.
Also noted but may be a seperate problem, the fan blower works, but will not direct flow to selected defog; upper or lower ducts.