Fuel System:
* Mass Airflow Sensor (MAF) Sensor: A failing MAF sensor provides inaccurate air readings to the computer, leading to a lean or rich fuel mixture. Intermittent failure would explain the inconsistent behavior.
* Throttle Position Sensor (TPS): Similar to the MAF, a bad TPS provides inaccurate throttle position data, resulting in poor fuel delivery. This is a common culprit for stalling, especially at idle.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing rough running, especially under acceleration when the engine demands more fuel.
* Fuel Pump: A weakening fuel pump might not supply sufficient fuel under load (acceleration) or at lower engine speeds (near stops). It could be intermittently failing.
* Fuel Injectors: A clogged or intermittently failing injector can cause misfires and rough running. This could be more noticeable under load.
* Fuel Pressure Regulator: A faulty regulator could cause inconsistent fuel pressure, affecting the mixture.
Ignition System:
* Ignition Coil(s): A failing ignition coil can cause misfires, leading to rough running and potentially stalling. Intermittent failure would match the symptoms.
* Spark Plug Wires: Cracked or worn spark plug wires can cause misfires, especially under stress.
* Spark Plugs: Worn or fouled spark plugs are a common cause of misfires.
* Distributor (if applicable): While less likely on a fuel-injected V6, issues within the distributor (rotor, cap) could lead to inconsistent spark delivery.
Other Possibilities:
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational speed and position. A faulty CKP can cause misfires and stalling.
* Vacuum Leaks: Vacuum leaks disrupt the air/fuel mixture and can cause rough running and stalling. Check all vacuum hoses for cracks or disconnections.
* Computer Issues (ECM/PCM): While less common, a failing engine control module can cause erratic behavior. This is usually diagnosed last after other more likely culprits are ruled out.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner (even a cheap one from an auto parts store) to retrieve any stored trouble codes. These codes will give you valuable clues.
2. Visual Inspection: Inspect all vacuum lines, spark plug wires, and connections for visible damage.
3. Check Spark Plugs and Wires: Inspect spark plugs for wear and fouling. Check the wires for cracks or damage.
4. Test MAF Sensor and TPS: These sensors can often be tested with a multimeter, but you might need a service manual or online resources specific to your vehicle to know the proper procedures.
5. Check Fuel Pressure: A fuel pressure gauge can help determine if the fuel pump is supplying adequate pressure.
Important Note: Since the problem is intermittent, it might require some patience to diagnose. The problem might only reveal itself under specific conditions. Keep detailed notes on when the problem occurs (engine temperature, load, etc.) to help pinpoint the cause. If you're not comfortable working on your car, take it to a qualified mechanic for diagnosis and repair.
