Average trip mpg fluctuating a lot

[xanderd]

Hi

Recently my average mpg readout on the digital dash has been fluctuating a lot.

 

It's the average one with a crossed out circle symbol, not the instantaneous one.

 

It used to take a very long time to change as it was averaged over a 600 mike trip, might go up 2mpg on a long trip for example.

 

But recently it jumped up from 46 to 50 on a 5 mike trip, then down to 24. Now it reads about 21 but it seems to change randomly, and far faster than it should.

 

No warning lights, 2011 model...any ideas?