Lifted from a post on ToyotaNation. Does yours use the OEM twin ground platinum electrode spark plugs? They are specifically used for the later model Gen 4s (camry) with twin coil packs and distributorless. These use a waste spark ignition, therefore the plugs fire twice during a 4 stroke cycle. If you use a single ground electrode, it will severely shorten the life of the plug. e.g. 6,000rpm on your camry engine will be like running 12,000rpm on another car, since the plug fires twice as often. You can also try double platinum plugs, i.e. plugs with a platinum chip also on the ground electrode. What happens in waste spark ignition is that 1 coil pack fires 2 spark plugs simultaneously, e.g. cylinder 1 and cylinder 4. So while one spark plug is firing normally, spark jumps from center electrode to ground electrode, the other spark plug is firing in reverse, i.e. from ground electrode to center electrode, therefore there is high wear on the ground electrode, this is where the platinum chip on the ground electrode gives longevity. Plugs like Denso Iridium SK20R11 and VK20 also have a platinum chip on the ground electrode. NGK Iridium IX and Denso IK20 dont.
