From all I've seen on the MPG thread and personal experience with my TSX it seems that the average MPG is a little overly optimistic. Is there anyway to calibrate this? I would say it is usually 1-2 MPG on the high side.

 

how on earth can u tell?

 

I keep a spreadsheet on fuel consumption and have verified that the read out on the trip computer is out by about 4 liters per 100km, so I guess that is about 1 gallon per 62 miles.

The trip computer tells me I am averaging 7 liters per 100kms measured over 6,000kms, but calculating from the spreadsheet the actual average is 7.4 liters per 100km

 

I also keep track of my fuel and I also notice that the mileage is 1-2mpg high.

 

Yep, same here.

 

mine is almost dead on. Less than .5 off each time.

18,000 miles and I check each time.

 

I find my MID to be 5 or 6% 'short' too, so your experience confirms mine.

I don't care to reprogram it, now that I know, I just work with it.

Glad you did such diligence on checking it though. Thanks.

 

On my last tank the MID was high by 2.9 mpg. Now I just subtract 3 mpg from whatever it tells me.

 

I think it's the nature of the beast. As long as it's about the same every time, you just work with it.
I think the biggest source of error is compression braking such as taking your foot off the gas while going down an off-ramp, etc. Your instantaneous mpg goes up to infinity because the injectors basically are shut off. If you have a lot of these on your normal drive, your error will be higher. That's my crackpot theory and I'm sticking to it.