Will not low idle

Tiny
STRETCH502
  • MEMBER
  • 1998 CHEVROLET TRUCK
  • 7.4L
  • V8
  • 2WD
  • AUTOMATIC
  • 12,324 MILES
454 tuned port fuel injection. It has no low idle. Start and let off gas and it shuts off. Hold rpm at 8 or 900 it runs fine pt it in gear and it goes down the road great let off gas to stop rpm goes down and it shuts off. Keep rpm at 800 or above all is good.
Thursday, August 16th, 2018 AT 7:10 PM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi and thanks for using 2CarPros.com.

This could be a few things. First, confirm there are no trouble codes stored in the system. If there are, let me know what codes are found. Here is a video showing how to scan for codes:

https://youtu.be/YV3TRZwer8k

Next, check for engine vacuum leaks. A leak can cause the engine to shut down at idle. Here is a link that shows how to check:

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

Finally, your vehicle has an idle air control solenoid (IAC). The IAC is designed to maintain engine idle speed when the throttle plate closes. The IAC is located on the throttle body of the vehicle. Here is a general link showing how one is replaced:

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

Here are specific directions for replacing the IAC on your vehicle. The attached pictures correlate with these directions.

___________________________________________

IDLE AIR CONTROL (IAC) VALVE REPLACEMENT
Throttle Position Sensor Electrical Connector

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.

__________________________________________________

I hope this helps. Let me know what you find or if you have other questions.

Take care,
Joe
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Thursday, August 16th, 2018 AT 8:21 PM

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