Some vehicle models will experience shaking after new spark plugs are replaced, and the shaking disappears when the old spark plugs are reinstalled. The reason is that the on-board computer has adapted to the ignition timing for large gaps, resulting in a mismatch between the ignition timing and the electrode gap of the new spark plugs.
Solution: Turn the car key to the ignition ON position (without starting the engine), press the accelerator pedal 15 to 20 times repeatedly, then turn the ignition off and back on, and repeat this process 5 to 6 times to reset the ignition timing. For some high-end vehicles with fault codes, a diagnostic computer is required to clear the fault codes.
