* Fuel Pump: When driving at highway speeds, the fuel pump works consistently to supply fuel to the engine. However, when you slow down and stop, the demand for fuel decreases. A weak or failing fuel pump might struggle to maintain sufficient pressure at lower engine speeds or idling. This lack of pressure can lead to fuel starvation, causing the engine to stall. The added stress of prolonged highway driving could exacerbate this problem.
* Clogged Fuel Filter: A clogged fuel filter restricts fuel flow to the engine. At higher speeds, the engine might still get enough fuel to run, but at lower speeds and idle, the restricted flow becomes insufficient, leading to stalling.
* Other possibilities (less likely given the circumstances):
* Ignition System Issues: While less likely to manifest only at low speeds after highway driving, a weak ignition coil or other ignition component could be failing under stress, worsening with the heat generated during prolonged driving.
* Sensor Problems: Various sensors (e.g., crankshaft position sensor, mass airflow sensor) regulate fuel delivery. A faulty sensor might provide incorrect readings, leading to improper fuel delivery, particularly noticeable at low speeds.
* Vacuum Leaks: A vacuum leak can disrupt the air-fuel mixture, affecting engine performance more significantly at idle than at higher speeds.
Why it's likely *not* something else:
Problems like a completely blocked catalytic converter would typically cause noticeable performance issues even at highway speeds. Similarly, major internal engine problems usually present with more consistent and severe symptoms.
What to do:
1. Check the fuel filter: This is the easiest and cheapest thing to check first. If it's visibly dirty or clogged, replace it.
2. Have the fuel pump checked: A mechanic can perform a fuel pressure test to assess the pump's performance at various engine speeds.
3. Have a diagnostic scan performed: This will read codes from your car's computer, helping pinpoint potential problems with sensors or other components. This should be done *after* you've checked the fuel filter, as a clogged filter is a very common cause.
Don't continue driving the car until this is resolved. Fuel starvation can damage your engine.
