This is a sign that the Throttle body injector are firing at the wrong event,inside the distributor is a reluctor that fires the TBI,they have a tendency to slip out of place,A new distributor is the solution for you, also keep the air cleaner on,
I have a friend who had this problem. At idle, everything seemed find, but as soon as you pressed on the accelerator and put van under load, stalling and backfiring. Tried a bunch of things. The one thing that fixed it instantly was replacing the ignition coil (next to the distributor). Nice and easy fix.