2001 Ford Taurus intermittent P0133 code and pinging

Engine Performance problem
2001 Ford Taurus 6 cyl Front Wheel Drive Automatic 35k miles

I think I have some engine pinging coming from the valve cover, I was using regular fuel always, I go on a long trip on the highway about once a week so I don't think it's carbon buildup however, my grandma owned the car until 2008 and probably never did much distance driving. I ve had the car for about 2 years and this problem just started. Anyways with premium fuel and octane booster the problem definitely almost stops, but is still barely noticeable at high rpms in 3rd or 4th gear. I have an intermittent p0133 code that has popped up twice and went away in a day or 2. I don't want to have to use premium fuel the rest of the cars life. What may be wrong? Where should I look first?