Looking at the graph also shows how P&G works. Lets say the driver is humming along at 2000rpm/35mph and can get 55mpg in that gear. By Increasing load while maintaining the same speed, via giving the engine lots of throttle and popping up to 40mph, the coasting down to 30mph, etc... the average BSFC can be near 300g/kWh instead of the ~425g/kWh at a cruise and mileage can be ~77mpg at the same average speed. The "increasing polynomial"/Road Load line can be broken up into the rolling resistance portion and aero resistance portion, like on page 6 of this (also includes driveline losses. If ya check out the rolling resistance and drive line losses portion, you may notice they are pretty much a straight line. This is kinda nice since it means that if we can cut our energy requirements at low speed in half, while still P&G'ing, we can just about double our mileage.

Its permanent. I'd need to replace it or replumb it. It as installed about 1.5 yrs ago.

There is no way it can run lean like this if its using the O2 sensor readings and excluding the IAT sensor readings to decide how much fuel to inject.

As for "P & G", i cosider it a dangerous waste of time. I think what is useful is a car that can go from point A to point B safely, at a reasonable speed (keeping with the flow of traffic), and using a MINIMAL amount of fuel to do it, without sacrificing engine life to do it.