A flashing check engine light and P0300 to P0312 diagnostic trouble code are surefire indications that one or more cylinders are misfiring. While occasional misfires may pass unnoticed, a steady misfire is hard to miss. The engine usually feels rough, lacks power and uses more gas than usual. Sometimes a misfire may feel like a vibration. A misfire also will cause a huge increase in hydrocarbon emissions, which can cause a vehicle to fail an emissions test.