Originally Posted by toast64

It sure appeared that there was another variable involved. So I decided to find out how long it took the meter to reset, as suggested on posts in this forum. What I found was surprising: the time it takes to recover from a manual reset varies - A LOT! After a few tests, I decided I had to try it under different conditions, because it seems to take a lot longer to reset when coasting! Here's roughly what I found:

The quickest it would reset was 4 seconds at 60-65 miles per hour on a flat road (from the time I let my finger off the reset button 'til it started registering mpg). At city speeds the reset time varied from about 6-10 seconds. Long coasts, however, were a different issue. While driving in the city, I once got 37 seconds before it registered mpg. My personal best was a whopping 57 seconds! I accomplished this by decelerating from 46 miles per hour down to 18 miles per hour while coasting, a total almost a mile! It was downhill until about 25 miles per hour when the road inclined back up. I was really surprised. I just kept going and going, and the mpg meter just kept giving me - - - - -. Finally at 18 miles per hour I pretty much had to accellerate or stop dead in the street, so I began to accelerate back up the hill. In about 4-5 seconds it registered the mpg.

So, this variable appears to have a lot of influence on the exact reset point. I'm now leaning towards it being a 100 km bug, that being the point where the reset begins. It apparently could come out of reset and begin measuring again anywhere from 4 seconds to 1 minute or more after the reset begins. But I don't have a way to run a test and control both variables. Maybe a passenger watching the trip mpg closely while going up or down a mountain could tell, but I don't have any mountains nearby.