Fuel System:
* Fuel Pump: A weak or failing fuel pump can't supply enough fuel to maintain idle, especially under load (like being in gear). This is a common culprit.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing similar symptoms.
* Fuel Pressure Regulator: A faulty regulator might not maintain correct fuel pressure, leading to inconsistent idle and stalling.
* Dirty Injectors: Clogged injectors can prevent sufficient fuel delivery.
* Fuel Leaks: A leak anywhere in the fuel system will starve the engine of fuel.
Ignition System:
* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational speed. A faulty CKP sensor can cause erratic idling and stalling.
* Cam Position Sensor (CMP): Similar to the CKP, a bad CMP sensor disrupts the timing and can cause stalling.
* Ignition Coil(s): A weak or failing coil can cause misfires, leading to low idle and stalling.
* Spark Plugs & Wires: Worn-out spark plugs or damaged wires can prevent proper combustion.
Air Intake System:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides inaccurate air/fuel ratio data to the computer, causing poor idling and stalling.
* Vacuum Leaks: Leaks in the intake manifold or vacuum lines disrupt the air/fuel mixture.
Other Potential Causes:
* Throttle Position Sensor (TPS): A faulty TPS provides incorrect throttle position information to the computer.
* Idle Air Control (IAC) Valve: The IAC valve controls idle speed. A dirty or faulty valve can lead to low idle and stalling.
* Transmission Issues (less likely): While less probable, transmission problems could put extra stress on the engine, contributing to stalling. This is more likely if the stalling only happens under load in certain gears.
* Computer Issues (PCM): A faulty Powertrain Control Module (PCM) can cause a wide range of problems, including stalling. This is usually diagnosed last.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored codes. These codes can pinpoint the problem area.
2. Visual Inspection: Check for obvious signs of leaks (fuel, vacuum, etc.), damaged wires, or loose connections.
3. Fuel Pressure Test: Measure fuel pressure to determine if the pump is delivering adequate pressure.
4. Check Engine Compartment for Vacuum Leaks: Listen for hissing sounds near the intake manifold and vacuum lines.
5. Test MAF Sensor and TPS: These can often be tested with a multimeter.
Important Note: Without proper diagnostic tools and experience, attempting repairs could worsen the problem. It's highly recommended to take the vehicle to a qualified mechanic for diagnosis and repair. Many of these components require specialized tools and testing equipment to properly diagnose. Ignoring the problem could lead to further damage.
