1991 CHEVY S10 4.3 ENGINE WANT IDLE OR STAY RUNNING WHAT CAN I TRY ?SEEMED LIKE I WAS OUT OF GAS PUT MORE IN DIDNT HELP CHANGED FUEL FILTER ,MAP CENSER, DIST CAP ROTOR BUTTON,VACUME LINES, OXYGEN WHAT NEXT?

Code 12 means you are in test mode, code 34 is a problem with the map sensor, and code 35 is a problem with the idle control valve.
But those two codes could show up if you disconnect those sensors or if the engine is having other problems.
In situations where the engine stalls, it is very easy to overlook something or assume a component is working.
Treat it like a no start. Pull a plug wire and watch the spark as the engine dies. Use carb cleaner or starting fluid to boost fuel supply.
You'll have to figure out if it is loosing spark or fuel to proceed.
Things like the coil, the stator in the bottom of the dist, or a relay can be the cause. Even low fuel pressure.

On electronic fuel injection pumping an pumping an pumping the gas pedal does nothing without the engine running ! Pushing the gas pedal to the floor will cause the PCM - engine computer to go into clear flood mode .

You have some very interesting ideas here , but not really how it works or is !

The vehicle will go into closed loop fuel control when the engine coolant temp reaches a definded temp an the O2 sensor get hot.

She would run for a couple minutes and die which is open loop when running, closed loop is when the sensors kick and it would die. Pulled spark plugs, they were black meaning no spark. Can only be 2

Black spark plugs indecate a rich condition , over fueled , wet spark plugs indecate no spark .

Thats what it sounds like.. Alot of times the pump will be pumping but not enough..

Have you checked the fuel filter?

I would run the fuel pump for a little while with the fuel line disconnected from the engine into a gas can . Although you might have changed everything you might still have residual water in lines or motor. I would still put dry gas in the tank

If it will start right back up and if you hold gas pedal will truck stay running ? if it will stay running when you hold the gas then replace the idle air control valve it is bad and cleaning it didnt help. but if it wont stay running even if you hold the gas pedal then the first thing is to make sure you are not loosing fuel presure

is it idling high and you put it i gear it runs rougher and smoke black check your coolant sensor also connection or sensor itself and fuel pressure if high check for return line blockage also vacuum leaks make sure you have the right vacuum going to your map sensor you need to check right vaccum at idle going to your map sensor/

try fuel filter and air filter

Have you changed the fuel pump yet?I had the same exact problem.I replaced my fuel pump with an AUTOZONE PIECE OF JUNK fuel pump.That pump lasted almost 2 days.The second day i had it the truck didnt want to start but it did and it ran like ****,and when i put it in gear it ran as long as I didnt touch that gas pedal.You could go get a fuel pressure test or just replace it,your call.You might want to check your filter too but im sure its the pump.Good luck

I put a new fuel pump, fuel filter, and a fuel pump relay and the fuel pump is still not coming on. I am not getting any fuel. Can you please tell me what it might be.