I recently had an oil change and air filter replaced.
The air filter is a generic filter not a sport, CAI or anything.
Now the car is averaging 1 to 1.5 more mpg in mixed driving.
I'm really pleased but I wonder if the system is reporting the mpg correctly.
Is this plausible ?

 

If you want to get real readings of your gas usage, do them yourself using math. Don't use the car's gauge- it's an estimate at best.

 

your oil change might've made a difference...?

i changed the oil in my bike and got an extra 10 mpg... granted it was the first oil change after break-in... but hey, if you have a new Z, maybe it's the same for you.

 

1.5mpg is just too small, all sorts of variables could net you that gain or loss. new filter shouldnt significantly increase your mpg unless your old filter was dirty as f.