I'm not sure if this matters, but the Platinums looked okay, color wise. When comparing them to a "spark plug t-shooter" photo, the coloring looked fine, not too lean, not too rich, just worn. Having just bought the car, I do not know when they were installed. By tuning the engine, what exactly do I need to do. I thought the timing was set, and could not be changed. Air/fuel mixture I guess could be checked. But with the fuel mileage that I am getting now, I am almost afraid to change anything. But in an effort to keep the MPG up what should I look for now? Not sure if it is relelvant, but the car does hesitate upon taking off, until it is warmed up 60-80 c. Perhaps cold start valve leaking and fouling plugs?