Will not stay running

Can you keep it running with giving more throttle?

Here is a guide that talks about this issue:

https://www.2carpros.com/articles/stall-at-idle

I am thinking there could be an issue with the IAC.

https://www.2carpros.com/articles/idle-air-control-valve-service

I am attaching the process below on how to replace this and reset the position.

You can try and clean this as showing in the guide above but if it were me, I would replace it. If there is no theft light issue then this would make the most sense.

Let me know if you have questions on this and what you find. Thanks

It won't stay running at all , throttle or not. But will start right up again immediately , just to instantly shut off again.

I will try the IAC replacement and let you know.

Thanks

Yeah. That sounds like an IAC. Sounds good. Please let us know what happens. Thanks for the update.

I pulled the IAC to check it , resistance was fine ( 45 - 55 ohms ) and it wasn't too dirty. so I cleaned it off and stuck it back in. Battery's dead again , so I couldn't start it to see if it worked. it's on the charger now and I'll let you know what happens.

Okay. Sounds great. If it was dirty then that could be it. These can fail in one of two ways. Either the solenoid side which is okay based on that reading or the valve sticks. If it makes any difference then you may still need to replace it. I have seen these still act up after cleaning so just be aware of that but let us know what happens. Thanks

Still won't run. Shuts off after a few seconds and can't keep it running with the pedal. I'm going to order a new IAC and hope that solves the issue . if not , do you think my ECM could be bad ??

If I might ask, you say it starts and runs a couple seconds but not any longer than that? And the battery keeps going down at the same time? That sounds like the typical bad GM instrument cluster, a chip in them fails and it prevents them from turning off so the battery goes down very fast, plus it can stop the security system from arming or notifying you that it has activated and you get the start run for a couple seconds and it shuts off routine.
Rebuilding or replacing the cluster usually takes care of the issue.

The battery didn't lose power all that fast , it took about 2 weeks ( and it's close to its 30 month guarantee. so I figure it's on its way out ). plus just the flashing light for the alarm would usually drain the battery down in about 3 weeks if I don't drive it. so I'm hoping the cluster will not be the issue.

I do appreciate any and all ideas of the why it won't stay running. I've had this truck over 10 years and thought I knew most of the ins and outs.

Okay, I just hear dead battery in a GM truck without a timeline and think of those great clusters... Anyway, try this, pull the fuel pump relay out and jump pins 87 and 30 , or if you know where the red pump prime connector is hiding (drivers side rear in the engine bay, usually taped to the harness), jump power to it and see if it stays running. If it now stays running it is starting on the prime and then running out of fuel. With it jumped you get constant fuel supply. That would tell you if it was PCM related or something else. The anti-theft in them shuts off the fuel pump but doesn't stop the prime at initial key on. The other item could be the PCM isn't seeing the rpm increase from the engine starting. It uses the oil pressure switch and the tach lead for those. No rpm increase or no oil pressure and it shuts the pump off.

Thanks , I'll try that this weekend.

Okay , so I jumped the relay ( could hear the pump running ) and still does the same thing , starts and runs for a few seconds and then shuts off. Tachometer and oil pressure both working for the few seconds it stays lit. so I don't think fuel is the issue. is there something that would shut down my ignition ?

I just replaced the crankshaft position sensor and have a new TPS and IAC on order. will give results after I install.

Thanks again for any and all ideas.

Nothing that normally operates that way. This doesn't have any aftermarket remote start or alarms on it does it? Some of those can be set up that way.
Beyond that you could pull a plug wire and see if it still has spark right as it shuts down. It really sounds like something is timing out and shutting it down. Have you tried a reset, pull the battery cables off and short them together, wait 2 minutes and reconnect. to the battery. See what it does then.

It does have an aftermarket alarm. pretty sure it only has the starter bypass and that's it.

I'll try the battery reset and check for spark.

Can I just hook up my timing light to the coil wire to check for spark?

Wouldn't the coil still fire (after the truck shut off) regardless if the distributor spinning or not?

Thanks

It fires based on the cam and crank signals, no signal, no spark. So the engine needs to be turning. See if you can look up the make and model of the alarm and verify how it's connected, IE what wire is it actually attached to.