I'm not complaining, but... The mpg on my 2003 350z coupe suddenly increased from 23 to 32 mpg with highway driving. I usually get 16 mpg city, and 23 highway. Nothing has been done to the car. No new fuel or tires.
Could this mean the failure of a sensor or pollution control feature?
Thanks

 

It just occurred to me that it could be AC failure, which I keep on all the time, even when not needed to keep things dry.

 

I don't remember the numbers, but I had a big jump in millage when I did a full tank of highway driving with no stops. I attributed it to a heavy right foot in 'city' driving. AC would only change millage by ~5%.