I gotta question guys, my mpg in my ls4 has been decreasing since I've got it, even after my tune I'm seeing less mpg, may be due to the tune idk yet but I switched from 87 to a 91 tune due to seeing the knocking charts, which is outrageous btw, but the question is is that my car is a 07, I'm sure no tune up has been done as far as plugs, maybe filter changes for tranny, but no plugs or wires, I'm not experiencing any misfires or hard idles, but could the plugs and it being over 5 years old at this point be a cause for a loss in mpg? Basically could u experience the loss of mpg without the misfire