* Rough running engine: The engine will run poorly, especially noticeable at idle or under acceleration. It might shake or vibrate excessively.
* Misfire codes: Your car's check engine light will illuminate, and a diagnostic code scanner will likely reveal a cylinder misfire code (P0300 for random misfire, or P0301, P0302, P0303, P0304 for misfires in specific cylinders 1-4 respectively).
* Reduced power: The engine will lose power and may struggle to accelerate.
* Hesitation or sputtering: The engine might hesitate or sputter when you accelerate.
* Poor fuel economy: You'll likely see a decrease in your gas mileage.
It's important to note that these symptoms aren't exclusive to a bad coil pack. Other issues like bad spark plugs, faulty ignition wires (though less likely on a coil-on-plug system), a failing crankshaft position sensor, or even a vacuum leak can also cause misfires. A diagnostic scan is the best way to pinpoint the problem.
