Most Likely Culprits:
* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine when it's idling. A dirty or faulty IAC valve prevents the engine from maintaining a consistent idle speed. Cleaning it is often a cheap and easy first step.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can provide inaccurate readings, leading to a lean fuel mixture and stalling. Cleaning it (carefully, with MAF sensor cleaner) is also a good first step.
* Fuel Injectors: Clogged or failing fuel injectors can prevent sufficient fuel from reaching the engine at idle. This would lead to a lean condition and stalling.
* Fuel Pressure Regulator: This regulator maintains the correct fuel pressure in the fuel rail. A faulty regulator could lead to low fuel pressure, especially at idle.
* Vacuum Leaks: Leaks in the vacuum lines can disrupt the engine's air/fuel mixture, causing it to stall.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can give incorrect readings, leading to poor idle and stalling.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum hoses and connections for cracks or leaks. Listen carefully around the engine for hissing sounds when the engine is running.
2. Clean the IAC Valve: Locate the IAC valve (usually near the throttle body). Carefully remove it and clean it with throttle body cleaner. Refer to a repair manual for your specific model to ensure you do this correctly.
3. Clean the MAF Sensor: Carefully clean the MAF sensor with MAF sensor cleaner. Use a light touch and follow the cleaner's instructions. DO NOT touch the sensor element with your fingers.
4. Check the Fuel Pressure: This requires a fuel pressure gauge and may need a professional mechanic. Low fuel pressure is a significant issue.
5. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any diagnostic trouble codes stored in the vehicle's computer. These codes can provide valuable clues to the problem.
6. Inspect the Fuel Injectors: This is more advanced and often requires specialized tools and knowledge. Visually inspecting for leaks or obvious damage is a start.
7. Check the Throttle Position Sensor (TPS): A multimeter can test the TPS's voltage output. This requires knowledge of the sensor's specifications.
Important Considerations:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Repair Manual: A repair manual specific to your 2000 Ford Expedition will be invaluable in identifying components and performing repairs.
* Professional Mechanic: If you are not comfortable performing these checks yourself, it is best to take your Expedition to a qualified mechanic for diagnosis and repair. This problem could be more complex than a simple cleaning.
The fact that the engine runs when you give it gas suggests a problem with the idle system, rather than a major engine problem. Start with the easier steps (cleaning the IAC and MAF) and work your way through the others. If the problem persists, professional help is recommended.
