Step on the gas and it will go down, release and it will go up. That is instantaneous reading - normal. The avg MPG will give you the reading for current trip / or current day (1) or since last time you reset (2).

 

Press the switch (up or down) on the end of the stalk to cycle back to your "average" MPG readout.

 

Well I tried out my MPG meter again on my ride home form work tonight, and it is definitely not working correctly. I know what its suppose to do, and how it should look but this thing is definitely screwed up! On my ride home is jumps every second from ---- to 200mpg. I also noticed that for a while it just sat at ----. I tried using the reset button, and I tried cycling through all the options a couple times, but it still is messed up. Everything else seems to work perfectly though, even the trip MPG. Weird!

 

Let's try this again. In the main readout (with the little "1" in the corner) you have two MPG display options; one averaged for the trip, the other instantaneous. The averaged one has a slashed circle at the beginning, the instantaneous does not. If you're in instantaneous mode, the number will change roughly once a second - on my car, I see values of perhaps 5-150 MPG, as I'm going uphill and down. Not very useful. Keep hitting up or down until you see the slashed circle, and see what it does.

 

Mine does exactly the same. Just ignore it now. And to my knowledge there is no mention of how to address this in the handbook.
Dave

 

It is normal for the real time reading to dramatically fluctuate.