High Probability Causes:
* Fuel Pump/Fuel Delivery: A failing fuel pump can't keep up with demand at highway speeds. The pump might be weak due to age or clogged by debris. A clogged fuel filter would have a similar effect. Low fuel pressure would cause stalling under load (like highway driving).
* Ignition System: This encompasses several components:
* Distributor Cap and Rotor: Worn or cracked components can cause misfires, leading to stalling. This is especially common in older vehicles.
* Ignition Coil: A failing coil can't produce the necessary high voltage to ignite the fuel-air mixture.
* Spark Plugs and Wires: Worn or damaged spark plugs or wires will cause misfires, particularly under stress.
* Mass Airflow Sensor (MAF) or Throttle Position Sensor (TPS): These sensors tell the engine how much air is entering and the throttle position, influencing fuel injection. A faulty sensor can send incorrect information, leading to a lean or rich mixture that causes stalling.
Medium Probability Causes:
* Vacuum Leaks: A significant vacuum leak can disrupt the engine's ability to run smoothly, particularly under load. Check all vacuum hoses for cracks or disconnections. This is harder to diagnose.
* Crankshaft Position Sensor (CKP): This sensor tells the engine where the crankshaft is in its rotation. A faulty CKP will cause the engine to misfire or stall.
Low Probability Causes (but still possible):
* Engine Cooling System: Overheating can cause the engine to stall as a safety mechanism. Check coolant levels and look for leaks.
* Transmission Issues (Automatic): While less likely to cause a sudden stall, transmission problems could contribute if the transmission is failing to provide power to the engine. This would likely be accompanied by other symptoms.
Troubleshooting Steps:
1. Check the Obvious: Start with the basics: fuel level, look for obvious damage to wires or vacuum lines.
2. Check Engine Light: If the check engine light is on, have the codes read at an auto parts store or mechanic. This can pinpoint the problem quickly.
3. Listen for Sounds: Any unusual sounds (knocking, ticking, whining) can give clues.
4. Professional Diagnosis: If you're not comfortable working on your car yourself, a mechanic can perform a diagnostic test to pinpoint the problem efficiently.
Because this is happening on the highway, it's crucial to address this issue promptly. Driving with intermittent stalling is dangerous. Don't attempt any major repairs yourself if you lack experience – it's best to have a professional diagnose and fix it.
