Fuel System:
* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A dirty or faulty IAC valve can cause rough idling. Cleaning it (with throttle body cleaner) is a relatively easy first step. If cleaning doesn't fix it, replacement is likely needed.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can lead to poor idle and erratic running. Testing is usually necessary to diagnose a TPS issue.
* Fuel Injectors: Clogged or leaking injectors can cause inconsistent fuel delivery, leading to rough idling. This is less likely to improve under load, but it's possible a partially clogged injector is only noticeably bad at idle. Testing or replacement may be needed.
* Fuel Pressure Regulator: This regulates fuel pressure in the system. A faulty regulator could cause erratic fuel pressure, leading to rough idle.
* Fuel Pump: A weak fuel pump might provide sufficient fuel under load but struggle at idle when demand is lower. This is less likely, but worth considering.
* Vacuum Leaks: Leaks in the vacuum lines can disrupt the air-fuel mixture, especially at idle. Inspect all vacuum hoses for cracks or disconnections.
Ignition System:
* Spark Plugs and Wires: Worn or fouled spark plugs and damaged spark plug wires can cause misfires, leading to rough running, particularly at idle. Replacing these is a relatively inexpensive and common fix.
* Distributor Cap and Rotor (if applicable): If your 4.3L has a distributor, cracks or corrosion in the cap and rotor can disrupt spark delivery.
* Ignition Control Module (ICM): This module controls the ignition system. A failing ICM can cause intermittent misfires.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational speed. A bad CKP can lead to erratic running.
Other Possibilities:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor can affect the air-fuel mixture. Cleaning it is worth a try.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can cause a build-up of pressure in the crankcase, affecting engine performance.
Troubleshooting Steps:
1. Check for vacuum leaks: Visually inspect all vacuum hoses and connections.
2. Replace spark plugs and wires: This is a relatively inexpensive and common source of the problem.
3. Clean the IAC valve: This is a simple and often effective solution.
4. Check the fuel pressure: This requires a fuel pressure gauge.
5. Inspect the distributor cap and rotor (if applicable): Look for cracks or corrosion.
If you're not comfortable working on your vehicle yourself, take it to a qualified mechanic. They can properly diagnose the problem and perform the necessary repairs. Providing them with the symptoms you've described will help them focus their diagnostic efforts.
