had the same. my case......i had change the plugs first (to the correct gap) it went away for a day then i came back. so i change the wires. no luck. after a week or so i pulled the plugs and the gap had widened to 50+.......it had gotten so lean(hot) that it started to heat the arm of the plug to the point of starting to fall off. but it had just widened before i caught it.