Car just rolled 50K and has new plugs and air filter installed by me about 2K ago. I did notice when I washed my car that my right exhaust tip was a little sooty and black and the other was clean and shiny. I have true duals now, so maybe an issue on pass side bank with plug wire or ????. Definately need to check into it, but car is running good so unsure where to go from here. Any suggestions???