* Worn Ignition Coils: Even if the plugs are new, the coils that provide the spark to the plugs can fail or weaken. A failing coil will cause a misfire in the cylinder it's connected to, leading to a skip or rough running. This is a common issue on Jeep Liberties of that era. This is probably the most likely culprit.
* Worn or Damaged Ignition Wires (if applicable): If your Jeep uses individual ignition wires (rather than coil-on-plug), these could be cracked, worn, or poorly connected, leading to a weak or intermittent spark.
* Dirty or Faulty Mass Airflow Sensor (MAF): A dirty MAF sensor provides inaccurate air/fuel mixture readings to the engine computer, leading to a rough running condition.
* Vacuum Leak: A leak in the intake manifold or vacuum lines can disrupt the engine's air/fuel mixture, leading to misfires.
* Fuel Injector Problem: A clogged or malfunctioning fuel injector can cause a cylinder to not receive the proper amount of fuel, resulting in a misfire. This is less likely given the relatively low mileage.
* Faulty Crankshaft Position Sensor (CKP) or Camshaft Position Sensor (CMP): These sensors tell the computer where the engine is in its cycle. A faulty sensor can cause misfires. Less likely but possible.
Troubleshooting Steps:
1. Check for Spark: If you're comfortable working on cars, you can use a spark tester on each cylinder to confirm if you're getting a strong spark at each plug. This will help eliminate the ignition coils and wires as potential culprits.
2. Inspect the MAF Sensor: Carefully remove the MAF sensor (look up the location in your repair manual) and clean it with MAF sensor cleaner. Don't touch the sensor element.
3. Listen for Vacuum Leaks: With the engine running, listen carefully around the intake manifold and vacuum lines for any hissing sounds that indicate a leak.
4. Professional Diagnostic: The most efficient method is to take it to a trusted mechanic. They can use a scan tool to check for any diagnostic trouble codes (DTCs), even if the engine light isn't on. Some codes might be pending, meaning a problem exists but hasn't triggered the light yet. They can also perform a cylinder balance test to pinpoint the source of the misfire.
Important Note: Ignoring a misfire can lead to further engine damage. It's best to address this issue as soon as possible. The ignition coils are a strong candidate to check first, due to their common failure rate in this vehicle.
