Fuel System:
* Clogged fuel filter: A dirty fuel filter restricts fuel flow, enough to allow starting but not sustained running.
* Low fuel pressure: The fuel pump might be weak or failing, unable to maintain sufficient pressure for consistent operation. This could also be due to a leak in the fuel lines or a faulty fuel pressure regulator.
* Faulty fuel injectors: Injectors may be clogged, leaking, or not delivering fuel consistently.
* Bad fuel pump relay: The relay that controls the fuel pump may be failing intermittently.
* Water in the fuel: Water in the fuel tank can cause the engine to stall.
Ignition System:
* Failing crankshaft position sensor (CKP): This sensor tells the computer the engine's rotational speed. A faulty one can prevent consistent ignition timing.
* Failing camshaft position sensor (CMP): Similar to the CKP sensor, but for the camshaft. An issue here will disrupt valve timing.
* Weak spark: Weak spark plugs or failing ignition coils can provide enough spark for initial starting but not enough for continued running. Worn distributor cap and rotor (if applicable) are also culprits.
* Ignition control module (ICM): This controls the spark, and a fault can lead to intermittent ignition.
Other Potential Causes:
* Mass Airflow Sensor (MAF) problem: A dirty or faulty MAF sensor provides inaccurate air readings to the engine's computer, leading to improper fuel mixture.
* Throttle Position Sensor (TPS) issue: A faulty TPS gives incorrect throttle position data to the engine computer, leading to poor fuel delivery.
* Vacuum leaks: A leak in the intake manifold or vacuum lines can cause a lean fuel mixture, leading to stalling.
* Engine coolant temperature sensor (ECT) fault: An incorrect reading from the ECT can lead to poor fuel mixture and stalling.
* Faulty PCM/ECM (Powertrain Control Module/Engine Control Module): The engine's computer itself could be malfunctioning. This is less common but possible.
* Security System Issue: Some vehicles have anti-theft systems that can prevent the engine from running if there's a problem with the immobilizer.
* Alternator problems: Though less likely to cause immediate stalling, a failing alternator might not be able to keep the battery charged and could cause stalling after a short period.
Troubleshooting Steps:
1. Check for diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any stored codes in the vehicle's computer. This is the most important first step.
2. Check the basics: Ensure you have enough fuel.
3. Listen for unusual noises: Any unusual clicking, whining, or sputtering sounds can point to a specific system.
4. Inspect visually: Look for obvious signs of damage, leaks, or loose connections.
Because there are so many possibilities, professional diagnosis with a scan tool is highly recommended. Attempting repairs without proper knowledge can lead to further damage or injury.
