intermittent engine start and die issue

[sbump]

I am having a problem that my truck will start but die immediately sometimes. Sometimes it will fire right up and be fine. I did find that if i give it gas/throttle immediately at start will likely will run and not die. Once the truck is running it seems fine and will drive. The start and die issue will happen when engine is cold or warm already. I am leaning towards a sensor issue like throttle position maybe but welcome any input/ help. Truck is 98 5.7.

 

[HotWheelsBurban]

I am having a problem that my truck will start but die immediately sometimes. Sometimes it will fire right up and be fine. I did find that if i give it gas/throttle immediately at start will likely will run and not die. Once the truck is running it seems fine and will drive. The start and die issue will happen when engine is cold or warm already. I am leaning towards a sensor issue like throttle position maybe but welcome any input/ help. Truck is 98 5.7.

Sounds like throttle position sensor to me. Has that, or the idle air control valve ever been replaced? Replaced both on my Burb last year (2019) about 2 weeks apart. Both the parts were original, with 175 thousand miles on them. Could also be the temperature sensor in the intake manifold under the thermostat housing. I'd replace the TPS first, much easier on the vortecs. 2 T20 torx screws on the side of the throttle body, and a connector. Hardest part is getting to it.

 

[sbump]

Sounds like throttle position sensor to me. Has that, or the idle air control valve ever been replaced? Replaced both on my Burb last year (2019) about 2 weeks apart. Both the parts were original, with 175 thousand miles on them. Could also be the temperature sensor in the intake manifold under the thermostat housing. I'd replace the TPS first, much easier on the vortecs. 2 T20 torx screws on the side of the throttle body, and a connector. Hardest part is getting to it.

Thanks for input. I’ll do that first. To my knowledge it is original.

 

[PlayingWithTBI]

Put a scan tool on it and see what kind of feedback you get from the sensors 1st. I'd check your fuel pressure too.

 

[stutaeng]

Do you have any codes? Could be fuel pressure, so check that. If fuel pressure is low you'd likely get lean codes if it's starving for fuel.

A scan tool that has live data is going to be ESSENTIAL to determine if sensors are working good. ECT, TPS, MAF, MAP, O2, and fuel trims can all be mostly ruled bad or good without even popping the hood. Essential for diagnosing correctly.

Short of that you can check most sensors with a DVOM, but it takes time. Check for ground, 12V, 5V and signal voltage. There's articles on how to do this. Very easy, but not ideal.


Many times same symptoms can be DIFFERENT issues.

 

[Eveready]

It probably would not hurt to check the integrity of the battery cables and battery ground. Sometimes all kinds of weirdness can arise from a simple thing like that. If the original cables are still in use it may be time to look at them seriously.

 

[IOWNJUNK]

Mine has done the same thing for years, shows code P1626 anti-theft fuel enable circuit.

 

[Chevy-SS]

I had a '98 K1500 5.7L. I agree with all above.

BUT just in case it's not one of the above issues, do you have a security light that flashes at all? My truck was doing similar to yours (not exact, but similar) and it turned out to be VATS issue, which I easily bypassed with a resistor. On the '98 truck, it's a simple little job, I have the diagram to do it, if you ever need to.

Again, I don't really think you have VATS issue... I would lean more towards what the other guys are saying... but if Security light is flashing, then it is likely VATS

 

[Steve A]

Pull and check the EGR valve, make sure you don't have a small piece of carbon holding the valve open.

 

[stutaeng]

Forgot to post the website on testing some of the sensors:

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/tp-sensor-tests-1

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/how-to-test-the-maf-sensor-1

https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-map-sensor-2

These are only a few of them. You can browse though the website to look at others. A test light, a DVOM with Hertz function and a vacuum pump/guage will go a long way in checking these without going full parts cannon approach.