The gas we get is intended for cars with oxygen sensors and automatically corrected fuel injection. So we have to deal with what we get. Depending on your driving habits you can make some adjustments with spark plug heat range. If a new plug solved your problem then I'd say the old plug was the problem. Here ya go, if you have future problems read the plugs .. or plug in our case.
http://www.gtsparkplugs.com/reading-...lug-color.html