start with the basics, compression test, leak down test, condition of spark plugs-black is rich mixture, plug wires, timing, vacuum lines, battery cables and terminals, positive connection at starter and ground connections at engine and body, also ground points in the wiring harness, pcv valve operation and the port that it connects to at the tbi (they are known for plugging up there), does the engine pick up rpm or drop rpm when the pcv valve is removed? make sure both injectors are pulsing a nice uniform cone spray into the tbi, check the timing as you rev it up to see that it does advance with rpm, make sure the rockers are all moving about the same (ensures you don't have a lobe gone off the cam).check for a plugged muffler or catalytic converter- do a vacuum test where you rev the engine up for a couple of minutes as you check to see if the vacuum goes down slowly. check at the exhaust pipe to see if it is black when it dies-too much fuel. check the fuel pressure in the inlet side of the tbi, maybe the regulator is shot. I had one that did this and it was actually the ecm. another one I did it was the ignition module.
like the guys say, give us as much info as you can so we can troubleshoot it without seeing it. what does it do when it stalls, is it like it is starving for fuel or does it does it run like you have the choke pulled out too far on a carbed engine-kind of lopey? does it black smoke out the exhaust and slowly die? does it stall quicklyas soon as it is placed into drive, like you dropped the clutch at idle in a standard shift truck, ? what have you checked already? have you tried cleaning the idle air control air passage or removed the idle air control motor and checked the pintle and seat for build up? have you removed and cleaned the throttle body and all the passages under it, like for the pcv valve port? have you checked the base timing with the timing connector unplugged and then with the connector plugged in to see if you are getting advance from the ignition module? have you checked for too much timing chain slack or has it maybe skipped a tooth on the timing set? turn the engine over by hand backwards about half a turn or whatever until it comes up on the timing marks. take the distributor cap off and make a mark on the distrubutor housing with a piece of tape or a crayon where the rotor is pointing to. then, while watching the igntion rotor, turn it over by hand the other way and note how many degrees the crank has to turn until the rotor just starts to move.that will give you an idea of how much timing chain slack you have. how many miles on the engine? has it been sitting around for awhile and now you are working with stale fuel? did it start this all of a sudden? if it did, did it start with some backfiring or anything specific?
hope this helps. keep us posted.