Other potential causes, though less likely, include:
* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate readings to the engine computer, preventing it from adjusting fuel and air correctly.
* Vacuum Leaks: Leaks in vacuum lines can disrupt the proper functioning of components involved in idle control.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor provides incorrect readings of air intake, leading to idle issues.
* Engine Computer (PCM): While less common, a faulty PCM can also cause problems with idle control.
* Fuel pressure problems: Although less likely given the symptom (it does run, just not at idle), low fuel pressure could contribute.
Troubleshooting steps (in order of likelihood):
1. Check the IAC valve: This is the most common culprit. It might be dirty, sticking, or failing. Cleaning it (with carb cleaner, following proper procedures) is a relatively easy first step. If cleaning doesn't work, replacement is necessary.
2. Inspect vacuum lines: Look for cracks, holes, or loose connections in all vacuum lines connected to the intake manifold and components related to idle control.
3. Check the TPS: A multimeter can test the voltage output of the TPS to see if it's within the specified range. Replacement is often the solution if faulty.
4. Clean the MAF sensor: Use a MAF sensor cleaner (never ordinary cleaners) and follow the instructions carefully. A dirty sensor can cause erratic readings.
5. Diagnose with OBD-II scanner: An OBD-II scanner can read trouble codes stored in the engine computer's memory. These codes will point towards the most likely problem area.
Important Note: Attempting to diagnose and repair automotive problems can be dangerous. If you are not comfortable working on vehicles, it's best to take the truck to a qualified mechanic. Improper repairs can lead to further damage or even injury.
