Gang, we're blessed with a 2011 Carrera GTS. The car came to its 4 year point in April with just 33,600 miles, but wanting to do the right thing to keep my Porsche CPO and extended (from a college frat brother) warranties in effect, this week the car went to Hoehn for a spark plug change. This is due at 40K miles or 4 years. I asked for, and got the removed plugs. They didn't look "that" bad. So today we had to drive up to the San Gabriel Valley - a 200 mile round trip.
We've put 4000+ miles on the car in the last year. Never got better freeway mileage than just over 20 mpg. Today, running typical I-5, 57, 60 speeds: 65 to 80 to some stop/go, guess what?? The car's computer is telling us we got just under 24 mpg! 3+ better than ever in the last year! That's 30-40 more miles for every 10 gallons!? This is the most overt mileage improvement I can recall from any of our many cars over many years, simply from changing plugs. FYI, the air filters are almost new, and never did we use cruise control.
Is this my imagination or are 997.2s and other late model Carreras super sensitive to spark plug changes