Most Common Culprits:
* Dirty Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty MAF sends inaccurate readings, leading to a lean or rich fuel mixture, resulting in rough idling and poor performance. Cleaning it (carefully, with MAF sensor cleaner) is often a simple and effective first step.
* Failing Ignition System: This includes spark plugs, wires, distributor cap (if equipped), and rotor. Worn or damaged components can cause misfires, leading to a rough idle and poor running. Inspect for cracks, corrosion, or worn-down electrodes.
* Vacuum Leaks: Cracks or holes in vacuum hoses can disrupt the engine's air/fuel mixture. Inspect all vacuum hoses for cracks, loose connections, or damage. Pay particular attention to the PCV system.
* Dirty or Failing Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A dirty or malfunctioning TPS can lead to erratic fuel delivery. Cleaning it (carefully) may help, but it might need replacing.
* Faulty Oxygen Sensor(s): These sensors measure the oxygen content in the exhaust and help regulate the air/fuel mixture. A faulty sensor can cause a lean or rich condition, resulting in rough running.
* Clogged Fuel Injectors: Clogged injectors can prevent proper fuel delivery, leading to a rough idle and poor performance. Cleaning them (professionally or with an injector cleaner) might resolve the issue.
* Low Fuel Pressure: Problems with the fuel pump, filter, or pressure regulator can result in insufficient fuel pressure, leading to poor running and rough idling.
* Faulty Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A dirty or malfunctioning IAC valve can cause erratic idling. Cleaning it might help, or replacement might be necessary.
Less Common, but Possible Causes:
* Engine Computer Issues: A failing PCM (Powertrain Control Module) or other related computer components can cause a wide range of problems, including rough idling. This is generally a more difficult diagnosis.
* Intake Manifold Leaks: Similar to vacuum leaks, cracks in the intake manifold can cause air leaks.
* Internal Engine Problems: In more severe cases, problems like worn valve lifters, low compression, or damaged rings can lead to rough running.
Diagnosis Steps:
1. Check Engine Light: If the Check Engine Light is on, have the codes read at an auto parts store (often free) to get a clue about the problem.
2. Visual Inspection: Inspect all visible components, looking for obvious signs of damage, corrosion, or leaks.
3. Basic Maintenance: Start with the easiest and cheapest options: check and clean the MAF sensor, inspect and replace spark plugs and wires if necessary, check vacuum hoses.
4. Professional Diagnosis: If the problem persists after trying the simple fixes, it's best to take your Expedition to a qualified mechanic for a proper diagnosis and repair. They have the tools and expertise to pinpoint the issue accurately.
Remember to always disconnect the negative battery terminal before working on any electrical components. Safety first!
