My 15 has both, but they seem to work exactly a like, both show avg. MPG and MPH while moving, but show dashes when stopped. I do not yet have a owners handbook so I cannot look them up. Can someone tell me the difference?

 

The instantaneous reading should be that - what mpg you are doing at that moment. It should vary pretty much instantly if you put your foot down. The auto gives you average mpg for the trip you are on. If you stop and turn off, it will start from scratch again when you re start the car.

 

This link may help:

https://www.ownerinfo.jaguar.com/