Possible Causes:
* Faulty Ignition Coil(s): This is a very common culprit. Even if the wires and cap/rotor are new, a failing ignition coil can prevent proper spark delivery to one or more cylinders. Testing each coil individually is crucial.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the engine's rotational position, crucial for proper ignition timing. A faulty CKP sensor can lead to misfires and stalling.
* Cam Position Sensor (CMP Sensor): Similar to the CKP sensor, but for the camshaft. A malfunctioning CMP sensor will disrupt ignition timing.
* Fuel System Issues: A weak fuel pump, clogged fuel filter, or problems with fuel injectors can cause intermittent misfires and stalling. Check fuel pressure.
* MAF Sensor (Mass Airflow Sensor): This sensor measures the amount of air entering the engine. A faulty MAF sensor can lead to incorrect fuel mixture, resulting in misfires.
* Vacuum Leaks: Leaks in the intake manifold or vacuum lines can disrupt the engine's air-fuel mixture, causing rough running and stalling.
* Throttle Position Sensor (TPS): A malfunctioning TPS can provide inaccurate information to the engine computer, leading to inconsistent fuel delivery.
Troubleshooting Steps:
1. Retrieve Diagnostic Trouble Codes (DTCs): Even with the parts replaced, there might still be stored codes. Use an OBD-II scanner to retrieve and record *all* codes, not just the misfire codes. This will give you more clues.
2. Coil Pack Testing: This is the most likely culprit after replacing the ignition components. Have a mechanic or use a multimeter to test each coil for proper resistance and output voltage. A visual inspection for cracks or damage is also important.
3. Check for Vacuum Leaks: Visually inspect all vacuum lines and the intake manifold for cracks or loose connections. Use a propane torch (carefully!) or smoke machine to detect leaks if visual inspection is inconclusive.
4. Inspect Fuel Pressure: Check fuel pressure using a fuel pressure gauge. Low fuel pressure indicates a problem with the fuel pump, filter, or fuel injectors.
5. Clean or Replace MAF Sensor: A dirty MAF sensor can cause erratic readings. Try cleaning it with MAF sensor cleaner (following the cleaner's instructions carefully) or replacing it if cleaning doesn't resolve the issue.
6. Check the CKP and CMP Sensors: These sensors can be tested with a multimeter or using an advanced scan tool to monitor their signals.
7. Inspect Throttle Position Sensor: Clean the TPS with electrical contact cleaner. If that doesn't help, you may need to replace it.
Important Note: If you're not comfortable working on your vehicle's electrical system or fuel system, take it to a qualified mechanic. Incorrectly diagnosing or repairing these issues can lead to further damage. The intermittent nature of the problem makes accurate diagnosis more challenging, so a professional inspection is highly recommended.
