My car wont run

Hi Gabro
try this procedure and let me know if it work.make sure the engine is in normal temperature, all accessories are off.
start the engine and let it idle for 1 minute.
put the selector into D and let the engine idle for 30 seconds.
turn the AC on and let the engine idle for 30 seconds.
turn the AC off and let the engine idle for 30 seconds.
put the selector into P and let the engine idle for 30 seconds.
switch engine OFF for 2 minutes.

check all the emissions vacuum system for leaks..

I suspect that your fuel system is faulty. Check for a clogged fuel filter, or if your fuel pump don't run at all, replace the "fuel pump relay". Fuel pump may be faulty. Sometimes your fuel pump will run, but be too weak to hold pressure, which will let your car idle somewhat, but be too weak to run the engine at speed or under load.

The pump is powered by the relay. The relay is grounded by the computer. It gets a ground signal for the first 3 seconds, then only if the computer sees oil pressure or RPM to know the engine is running.
You should be able to ground the relay and run the pump for several minutes. After 30 seconds you should be at max pressure.
Normal pressure is 15psi for a truck that has throttle body injectors such as a mid 80s model, and 65psi for trucks that have port fuel injection like yours.
You may have the wrong pump.

Try some fuel stabilizer in the fuel tank.Then i would take mass air flow sensor and the idle air control sensor off and clean them using a non-chlronated brake cleaner.Then reset the computer by disconnecting the ground cable on the battery for 30 seconds.

Once the battery voltage gets too low to run the ignition system then the engine will die,like you said.You need to get the alternator repaired or replace the control module that replaced the voltage regulator on these trucks.Either way,the truck is not charging the battery and it needs to be.

Try resetting the ECM, turn the ignition key to the on position "engine not running" and pull the fuse to the ECM and place it back in. Leave the keys in that position for 30 seconds and then turn it off and on again for 5 seconds and start. this will reset the ECM to default. It may stall again but let it, just start it again and let idle for 3min and go foe a test drive. This should reset the way the engine and transmission performance, and should reset the idle issue on your Envoy. Good luck and keep me posted.

idle stepper motor(IAC) controls idle speed it is located on throttle body
IDLE LEARN PROCEDURE
Whenever the battery cables, the electronic control
module (ECM), or the ECM fuse is disconnected or replaced,
the following idle learn procedure must be performed:
1. Turn the ignition ON for 5 seconds.
2. Turn the ignition OFF for 5 seconds.
3. Turn the ignition ON for 5 seconds.
4. Start the engine in P/N (park/neutral).
5. Allow the engine run until the engine coolant is
above 85_C (185_F).
6. Turn the air conditioning (A/C) ON for 10 seconds, if
equipped.
7. Turn the A/C OFF for 10 seconds, if equipped.
8. If the vehicle is equipped with an automatic transaxle,
apply the parking brake. While pressing the
brake pedal, place the transaxle in drive (D).
9. Turn the A/C ON for 10 seconds, if equipped.
10. Turn the A/C OFF for 10 seconds, if equipped.
11. Turn the ignition OFF. The idle learn procedure is
complete.

Check your fuel pump presure. Pump is in the tank. Also try and loosen the fuel cap, the tank vent may be stopped up.

fuel filter or dirty or clogged injectors