Platinum plugs come from racing technology, if you run long distances at high speed they work fine. However, if one stops often and idles while sitting, they soot up. I thought the idea ridiculus until last week. My 380SL would miss after idling for a minute. My mechanic started looking things over and I told him I had just put in new platinum plugs. He immediately raised up, went over to the shelf containing plugs and exclaimed that was the problem. He put in new W8's and sure 'nough, problem cured. I don't know if the new '+ 4' plugs are better, but I think I'll pass from now on. My car, too, was rich and idled black smoke. It needed to be leaned out. FWIW.