If you have a dodgy O2 sensor on the other bank, then it will also probably throw things out....
I'm currently on a fill-empty cycle to see what my mileage is like on gas. Now it's running a somewhat properly I filled up before Summer Camp and got 60L into the tank, which meant I had a total fill of about 75L.
Including the to/from summer camp, and the trip down to London yesterday, I'm up to about 150miles on the trip computer.
I got to about 160miles last time before I filled up and I reckon I had about 15L left.
Computer in the RR showed an MPG of 14.3mpg before I came to London, and showing 15.0 when I arrived.
I'm going to run it on gas tomorrow until I get to 200 miles (about half way home I think) or until it runs out and switches back to petrol - whichever comes first! Then I'll refill when I get home and post my figures up too.
I think it might be running a touch lean still under load as 50-70mph acceleration is a bit gutless, but I think it is also doing it in top gear with the torque converter locked up unless I really poke the throttle.
Figures in a couple of days...