91 Lumina stalling probem

I have a 91 Lumina APV with a 3.1 L engine that was brought from Georgia. The problem I have is that it keeps stalling. It sat for 9 months over the winter here in Wisconsin. I have replaced the ICM, the TPS, The coil pack and serviced the EGR valve and gave it a complete tuneup. There is good gas flow throught the injectors into the throttle body. The fuel pump and filter were replaced 4 months before it was parked and it ran fine then. Fresh gas was put in with no luck. There are no error codes from the computer prom yet I can't keep it running. What else could I be missing.
I want to sell it, but not until I can trust it to run properly. Any help would be appreciated. Thanks.

What comes to mind right away is something I read a while back that stated something I've noticed myself. Up to 90% of sensor/computer releted performance and stalling issues can be traced back to improper grounding and connection issues. Especially on a vehicle that has sat, unused for some time. I always begin with the basics. Verify (don't just look at) the battery connections. Find all the ground straps that run from engine to body, etc. and make sure they aren't broken or corroded. Take apart EVERY connector you can reach, shoot a little WD-40 on the terminals and plug it back in. Note as you do if any wiring is sagging into anything hot or moving, due to broken or missing plastic supports etc. Make sure all the connectors have that little plastic key in them, if they are supposed to have one, and if missing, run a zip tie through it where the key would go. You would be amazed how many "phantom" problems will dissappear after this treatment, even if you don't actually find anything you can point to and say "that was the problem!" Computer controlled cars rely on microvoltage readings, and any loss of grounding or temp induced resistance changes can be critical. Good luck!

P.S. you can try driving it with some jumper cables running from the negative battery post to the engine block and see what happens. If the problem is gone, you need to start looking for the broken strap. I think there is a bundle of ground wires on that which go to the thermostat outlet bolt, sometimes they are really cruddy. Separate, clean and rough 'em up and try it again.