Stalls at idle

We need to start with check fuel pressure. Let's hook up the gauge and turn the key on and just let it sit there for 15 minutes. I want to see what the pressure is and then how quickly it bleeds off.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

I am thinking you have injector issues. If it is leaking fuel then it would cause the RPM to go real high and then the stall is either due to too much fuel or not enough. So let's start with this and go from there. Thanks

Hi,

This could be the result of a few different things. First, check to see if there are any engine vacuum leaks. Here is a link that shows how to check:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Next, the idle air control valve (IAC) is responsible for maintaining engine idle speed. It is located on the throttle body. I attached two pics below (pics 1 and 2) showing the location. The IAC allows a metered amount of air enter the engine when the throttle plate is closed. So, if it is not functioning or is clogged with carbon, it will cause a problem

Here is a link that explains how to service the IAC:

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

If you determine it is bad, here are the directions for replacement. The last section below will indicate the relearn process.

These directions also explain how to inspect it.

_________________________________

1996 Chevy Truck C 1500 Truck 2WD V8-5.7L VIN R
Idle Air Control (IAC) Valve Replacement
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Speed/Throttle Actuator - Electronic Service and Repair Procedures Idle Air Control (IAC) Valve Replacement
IDLE AIR CONTROL (IAC) VALVE REPLACEMENT
Throttle Position Sensor Electrical Connector

pic 3

pic 4

pic 5

pic 6

REMOVAL PROCEDURE
1. Remove the electrical connector from the Idle Air Control (IAC) valve
2. Remove the IAC valve attaching screws.

CAUTION: If the IAC valve has been in service: DO NOT push or pull on the IAC valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also, DO NOT soak the IAC valve in any liquid cleaner or solvent, as damage may result.

3. Remove the IAC valve assembly.
4. Remove the O-ring.

CLEANING AND INSPECTION PROCEDURE
1. Clean the IAC valve O-ring sealing surface, pintle valve seat, and air passage.

Use the carburetor cleaner and a parts cleaning brush in order to remove carbon deposits. Follow instructions on the container.
Do not use a cleaner that contains methyl ethyl ketone, an extremely strong solvent and not necessary for this type of deposit.
Shiny spots on the pintle or seat are normal. They do not indicate misalignment or a bent pintle shaft.
If air passage has heavy deposits, remove the throttle body for complete cleaning.

2. Inspect the IAC valve O-ring for cuts, cracks, or distortion. Replace if damaged.

NOTE: If installing a new IAC valve, replace with an identical part. The IAC valve pintle shape and diameter are designed for the specific application.

3. Measure the distance A between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure in order to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

MEASUREMENT PROCEDURE

NOTE: If installing a new IAC valve, replace with an identical part. The AC valve pintle shape and diameter are designed for the specific application.

Measure the distance A between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure in order to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

INSTALLATION PROCEDURE
2. Lubricate the IAC valve O-ring with clean engine oil.
2. Install the IAC valve assembly.
3. Install the attaching screws.

Tighten
Tighten the IAC valve attaching screws to 3.0 Nm (26 lb. in.).

4. Install the electrical connector.
5. Reset the IAC valve pintle position.

5.1.Turn the ignition switch to the ON position for 5 seconds.
5.2.Turn the ignition switch to the OFF position for 10 seconds.
5.3.Start the engine.
5.4.Check for the proper idle operation.

_______________________________

Reset directions:

1996 Chevy Truck C 1500 Truck 2WD V8-5.7L VIN R
Idle Air Control (IAC) Reset Procedure
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Speed/Throttle Actuator - Electronic Service and Repair Procedures Idle Air Control (IAC) Reset Procedure
IDLE AIR CONTROL (IAC) RESET PROCEDURE
1. Turn the ignition switch to the ON position for 5 seconds.
2. Turn the ignition switch to the OFF position for 10 seconds.
3. Start the engine.
4. Check for the proper idle operation.

___________________________

Let me know if this helps or if you have other questions.

Take care,
Joe

Okay. So it shut off and now when you turn the key it starts and revs up and then stalls?

If so we need to check the fuel pressure. This sounds like an injector issue. Basically when you turn the key it builds the pressure and if an injector is leaking it will dump a lot of fuel and the engine revs up and it stalls the engine due to too much fuel.

Also, we may have a fuel pressure issue due to a pump issue so let's check fuel pressure and go from there. Thanks

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Okay. We need to check 3 things. Even though you replaced these sensors that doesn't correct for an air restriction or faulty IAC. So Joe attached the info on the IAC which is different then the TP sensor or the mass air flow sensor. We need to remove that and clean it or replace it. The reason is, you are holding the throttle open which is bypassing the IAC and allowing more air to come in. So if the IAC is not allowing the proper amount of air in it will not allow the engine to keep running.

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

Next thing is to check fuel pressure just to eliminate it. You may be correct that this is not the issue but the only way to know is to check the pressure. Otherwise we are assuming it is okay and I have been burned too many times to not just check the pressure to make sure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Lastly we need to check the air intake system for restrictions or carbon build up. This relates to the cleaning of the IAC but we need to check the simple things like the air filter as well. In addition to this is to check the intake for vacuum leaks.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let's check these three things and go from there. Thanks