My 4Runner has a panel-mounted display that displays, among other things, MPG (see photos of "FourRunner"). I have tried pressing buttons in different combinations till the cows come home, however, and all I can get it to display is average MPG. I press the "Mode" button and it cycles through the options, but only average MPG.
Somebody mentioned that it can also display instantaneous MPG: I am wondering if that's something you have to specifically enable - via secret button combination, jumpers, dip switches, etc - as a "safety" issue. I.e., so Toyota doesn't get sued because you spend all your time looking at the gauge and run into the car in front.