Does a CAI improve the gas mileage? How much?

 

A CAI could improve gas mileage. If you see an increase, it will be after at least 2 months. I say this because for 2 months after you install it, you will spend more time with your pedal to the floor than off the floor. Then you start to get a little less excited about the sound.
Get one though, the sound is incredible.

 

Technically yes, because the engine has to work less to get the air it needs. Realistically no, because for one, you'll be on the gas more to hear/feel it, and even if you drive it very conservative, the MPG gains will be pretty minimal.