Dies without throttle until warm

[Rustjunky67]

I posted a reply to a thread I had covering my long process of learning about this motor and haven't received any responses and I also think this situation is one that may help others because 99% of what I find is the opposite of what I'm experiencing.
94 k1500 5.7TBI NV4500 transmission.
What I have going on is that I can crank and start the engine, it will immediately fire up when cold as soon as I hit the key and will run great at about 1500 rpm. But as soon as rpm starts dropping and hits 1000 it dies as if I switched it off. It may start back and ONLY stay running WITH throttle applied until it warms up OR it may require starting fluid to start back up and ONLY stay running with throttle applied until it warms up. In both instances, it runs kinda rough.
After it gets warm, however, it runs smoother than it ever has and has more power than it has since I've owned it (I can smoke 2nd when previously it would barely do that on dirt). And continues to start and stay running until it's cold again. Idles so smooth between 550-600rpm that you have to make sure it's still running. I cannot figure it out to save my life.
Surely someone else has experienced this and can point me in the right direction.
Thanks guys

 

[Schurkey]

How old are the usual "tune-up" items? Cap, rotor, plug wires, spark plugs, fuel filter, air filter, verify base ignition timing, electronic timing advance, PCV system, heated-air intake system, etc?

What is the fuel pressure when the engine stalls? When it runs good?

Connect a scan tool, verify ALL sensors and computer outputs, especially IAC, coolant temp sensor, TPS, and fuel trims including when it stalls.

Is the magnet on the distributor shaft cracked as is common with TBI distributors?

 

[GoToGuy]

Are you using the using the OE service manual? There is a great section on diagnosis of unusual operating circumstances. That information with troubleshooting feedback might get the correct repair. Guessing and changing random parts will eventually get you there but at what extra cost? Approach the problem in a logical orderly fashion. It might take a little time, but random part changing without a clear plan only gets you lost time and money and more spares on the parts shelf.
Is it a sign of weakness to have to read and follow the words written by the people who designed these trucks.

 

[Rustjunky67]

Ihave gone through every diagnosis and repair and service manual. Have you not noticed that there are about 5 or 6 parts and about 5 or 6 problems that are mentioned in EVERY SINGLE issue on a tbi? And usually unless you find the exact combination that works for your particular truck it doesn't matter what you change out? Trust me I've read and gone through every possibility I can before I post on any forum most times. Thanks anyway

 

[1997]

is everything stock, no mods?
94 TBI uses some old school "stuff" when cold, ie air cleaner with a flapper and heater tube from exhaust manifold when cold. everything intact?

maybe some info here .... https://www.gmt400.com/threads/95-k1500-350-tbi-bogging-down-when-air-temperature-is-cold.60961/

02 sensor new?

 

[GrimsterGMC]

Ihave gone through every diagnosis and repair and service manual. Have you not noticed that there are about 5 or 6 parts and about 5 or 6 problems that are mentioned in EVERY SINGLE issue on a tbi? And usually unless you find the exact combination that works for your particular truck it doesn't matter what you change out? Trust me I've read and gone through every possibility I can before I post on any forum most times. Thanks anyway

When I bought my truck it was the first vehicle I owned with a computer and required a whole new why of thinking when diagnosing problems. I don't know the correct term but I call it the daisy-chain effect. When 1 sensor starts to fault the computer will make adjustments to others to compensate, that can then give the impression that something else is going on. So you use your best logic to understand what's happening and think you have it worked out and fit new parts only to find it makes no difference, you keep doing this until you finally hit on the real problem. This is also hampered by getting new parts that don't work right out of the box so you wrongly assume they can't be the fault. You are quite correct when you say that it is the combination of parts all working together that really matters.

 

[Rustjunky67]

How old are the usual "tune-up" items? Cap, rotor, plug wires, spark plugs, fuel filter, air filter, verify base ignition timing, electronic timing advance, PCV system, heated-air intake system, etc?

What is the fuel pressure when the engine stalls? When it runs good?

Connect a scan tool, verify ALL sensors and computer outputs, especially IAC, coolant temp sensor, TPS, and fuel trims including when it stalls.

Is the magnet on the distributor shaft cracked as is common with TBI distributors?

Brand new everything... fuel pressure is 15 constant, except when off of course.
But for it to run so perfectly then just stop dead. And after that rough idle until motor warms up then running and idling perfectly until motor is cold then same process over. I don't have scan tool nor access to one nor knowledge to use it. As I mentioned in anther reply, there seem to be 5 to 6 common problems that have 5 or 6 parts mentioned as the solution to EVERY SINGLE ONE OF THE PROBLEMS that worked for somebody at some time. So I am aware of the usual suspects lol... just hoping to find someone with some direction to head for this particular problem as it is the opposite of what most experience, which is stalling once warm. Mine is stalling UNTIL warm.

 

[Rustjunky67]

is everything stock, no mods?
94 TBI uses some old school "stuff" when cold, ie air cleaner with a flapper and heater tube from exhaust manifold when cold. everything intact?

maybe some info here .... https://www.gmt400.com/threads/95-k1500-350-tbi-bogging-down-when-air-temperature-is-cold.60961/

02 sensor new?

Yessir that tube has never been present on this truck since I've owned it and never had any issues

 

[Schurkey]

I don't have scan tool nor access to one nor knowledge to use it.

Take it to someone who does.

The alternative is a crystal ball, or throwing parts at it semi-randomly.

hoping to find someone with some direction to head for this particular problem as it is the opposite of what most experience, which is stalling once warm. Mine is stalling UNTIL warm.

Most-likely suspects, not in any special order:
IAC
Faulty ECM/faulty PROM
TPS
Coolant temp sensor

High-humidity, ~40 degrees ambient temp could be throttle icing since there's no heated-air intake. Colder than 32, probably not. Warmer than 50, probably not. Low humidity, probably not.

Find someone to connect a scan tool, look at the data stream.

 

[df2x4]

Looks like the community Snap-On scan tool has reached the end of the list of people who needed to use it, you could sign up in that thread and get on the list.

https://www.gmt400.com/threads/gmt400-community-scan-tool.60565/page-19