High-Probability Issues:
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer the position of the crankshaft. A faulty CKP sensor will cause erratic timing, leading to a rough idle and misfires, especially at higher RPMs when the engine demands more precise timing. This is a very common culprit in these symptoms.
* Cam Position Sensor (CMP): Similar to the CKP, a bad CMP sensor provides incorrect information about the camshaft's position. This also severely impacts timing and can cause misfires across the RPM range.
* MAP (Manifold Absolute Pressure) Sensor: This sensor measures the air pressure in the intake manifold. A faulty MAP sensor can lead to incorrect fuel delivery, causing a rough idle and poor performance, potentially manifesting as a misfire at higher RPMs.
* Throttle Position Sensor (TPS): A malfunctioning TPS won't accurately report throttle position to the engine computer. This can cause erratic fuel delivery and ignition timing, resulting in rough idling and poor performance.
* PCV Valve (Positive Crankcase Ventilation): A clogged PCV valve can build up pressure in the crankcase, affecting engine performance and potentially causing misfires.
Medium-Probability Issues:
* Fuel Injectors: A clogged or malfunctioning fuel injector can lead to insufficient fuel delivery to one or more cylinders, causing misfires. This is more likely to show up as a consistent misfire in a specific cylinder, but could contribute to overall roughness.
* Fuel Pump/Fuel Filter: A weak fuel pump or clogged fuel filter might not deliver enough fuel under high demand (high RPMs).
* Oxygen Sensor(s): While less likely to directly cause a misfire, a faulty oxygen sensor can lead to a rich or lean fuel mixture, affecting idle and overall performance.
Low-Probability Issues (but still possible):
* Intake Air Leaks: A leak in the intake system can disrupt the air/fuel mixture, leading to erratic running.
* Compression Issues: Low compression in one or more cylinders could cause misfires, but this is less likely if the problem started after the ignition components were replaced. A compression test would be needed to diagnose this.
* Wiring Harness Issues: Although you've replaced the coil pack and wires, there could be damage elsewhere in the wiring harness affecting the signals to or from the various sensors or injectors.
Troubleshooting Steps:
1. Check for diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any stored codes. This will often point directly to the failing component.
2. Visual Inspection: Inspect all vacuum lines and hoses for leaks or cracks. Check the fuel lines and connections.
3. Sensor Testing: If you have a multimeter, you can test the voltage output of the sensors (CKP, CMP, MAP, TPS) to see if they're within the manufacturer's specifications. This requires a bit of technical knowledge.
4. Fuel Pressure Test: Measure fuel pressure to rule out fuel delivery problems.
5. Compression Test: This is more involved but will check the health of your cylinders.
Recommendation: Start with checking for DTCs using an OBD-II scanner. This is the quickest and easiest way to narrow down the possibilities. If no codes are present, then systematic testing of the sensors mentioned above is the next logical step. If you're not comfortable doing this yourself, take it to a qualified mechanic. It's much cheaper to diagnose the issue correctly than to continue replacing parts randomly.
