Each Lexus spark plug must be firing the same amount of voltage in the correct heat range or the engine will run rough. With properly working spark plugs in each cylinder on your luxury vehicle, a smooth ride can be enjoyed by the occupants. The Lexus spark plug is the end component for your ignition system on your engine. The path for the spark generation on the new models of Lexus begins with the on board computer which sends a signal to the ignition coil through the spark plug wires resulting in an arc of electricity at the end of the plug. On Lexus models from the early 1990s there was a distributor in the ignition system. All of these ignition components must be in proper working order for the spark plug to generate a strong arc so that the air/fuel mixture can ignite and combust. The way to check the arc at the plug on your Lexus has not changed since the internal combustion engine was first introduced over 100 years ago. An exposed plug must be grounded out on the engine so the spark can be observed. If there is any faulty part in the ignition system, it will show up as a weak or none existent spark. When performing this check, make sure you do not damage the plug wire. After time the boot on the plug wire can become fused to the plug and be difficult to disengage on your Lexus engine. So the wire stays intact, the boot should be twisted on the plug like unscrewing a light bulb about a 1/4 turn before you pull it. This will free it up so it can be safely pulled from the spark plug without damaging the wire.