I’ve been spending some time on this recently and have made some progress.
Firstly the tyre size correction has helped with the MPG displayed “looking better” than before. I was getting 22mpg before, and with the correct tyre size it reported 26mpg.
These comparisons were made on an easily repeatable journey where the only real difference between them would be the outside temperature.
As mentioned before, i have also had my EGR disabled and blanked. This has given me another 4mpg on my car, and drastically improved throttle response! My car now reports 30mpg for typical driving, with a “low” of 28 with a more heavy rough foot! Brimming the tank and calculating the mpg now shows i am doing an actual 26mpg. More time is needed to get a truer reflection of actual mpg of course…
Things have certainly improved, and i think the next item that will make a difference are the tyres. Swapping for a decent brand with less noise / drag should make a different. Even if only by a few mpg… Currently driving: 2012 L322 SE Overfinch 4.4 tdv8
2014 Audi Q7 3.0d (good riddance)
2010 L322 Autobiography 5.0 Supercharged
2011 L320 HSE 3.0 sdv6
2014 Jaguar XF-RS 5.0 supercharged
2007 BMW 535D
2005 Mini Cooper S