On my probe, I was running NGK wires, and Denso Iridium plugs. The Iridium plugs are the ones used in race cars. After I put them in, I was amazed, my idle was really smooth, and the car had a tad bit more kick when accelerating, and was really smooth. The plugs, though, cost between $13 and $25 a piece. Maybe I'll try a set on the cougar. Some car don't respond well to platinum, that's why I was asking.