Common Causes:
* Dirty or Failing Mass Airflow Sensor (MAF): The MAF sensor measures the air entering the engine. A dirty sensor provides inaccurate readings, leading to a lean or rich fuel mixture and a rough idle. Cleaning it (carefully, with MAF sensor cleaner) is often a first step. If cleaning doesn't work, replacement might be necessary.
* Dirty or Failing Throttle Body: Similar to the MAF, a dirty throttle body can impede airflow. Cleaning it with throttle body cleaner is often a simple solution. If it's severely worn, it might require replacement.
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs and/or ignition wires can cause misfires, resulting in a rough idle. Check for wear and tear, and replace them if necessary. Pay attention to the gap on the spark plugs, it must be correct.
* Vacuum Leaks: Small cracks or holes in vacuum hoses can disrupt the air/fuel mixture, causing a rough idle. Inspect all vacuum hoses for damage.
* Failing PCV Valve: The Positive Crankcase Ventilation (PCV) valve helps vent pressure from the crankcase. A failing valve can lead to excessive pressure build-up and a rough idle. It's a relatively inexpensive and easy part to replace.
* Dirty Fuel Injectors: Clogged or dirty fuel injectors can cause an inconsistent fuel supply, leading to a rough idle. Cleaning them (professionally or with a fuel injector cleaner) might be necessary.
Less Common Causes:
* Faulty Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation. A faulty CKP can cause major issues, including a rough idle.
* Faulty Cam Position Sensor (CMP): Similar to the CKP, but for the camshaft.
* Ignition Coil Issues: One or more ignition coils might be failing, leading to misfires in individual cylinders.
* Fuel Pump Issues: A weak or failing fuel pump can't supply enough fuel at idle.
* Air Intake Restriction: A clogged air filter restricts airflow, affecting the air/fuel mixture. Replace it if it's dirty.
* Engine Mounts: Worn engine mounts can allow excessive engine movement, leading to a rough idle (though this is less likely to be the *sole* cause).
Troubleshooting Steps:
1. Check the basics: Start with the easiest things – clean the MAF sensor and throttle body. Replace the air filter. Inspect vacuum hoses.
2. Listen to the engine: A specific cylinder misfire will often sound like a distinct "chugging" sound.
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored by the car's computer. These codes can provide valuable clues.
4. Consult a mechanic: If you're not comfortable diagnosing the problem yourself, take your Mustang to a trusted mechanic. They have the tools and expertise to pinpoint the cause and make the necessary repairs.
Remember that a rough idle can be a symptom of multiple underlying problems. A systematic approach, starting with the most common causes, will help you efficiently diagnose the issue.
