[Cardinal Grammeter]

OldBeaver and others,

RE: Scion MPG function of Throttle Position.

There was no "thinking" involved in this since it was a direct observation.

I drove the car for 4 hours over big hills and across deep valleys and the instantaneous MPG readout in the dash could literally be "set" by "adjusting" the throttle pedal.

If you wanted 50 mpg, just press the pedal 1/32 or an inch.

It did not matter if you were losing speed going up a hill or gain speed going down a hill. The mpg did not change if you did not change the pedal position.

So the "game" became, "What minimum pedal position (max MPG) will be necessary to crest this next hill at 30 mph?"

When I could see a valley where I would be going from one hilltop to another, I would "set" the MPG around 45 (very small pedal position) and let the car build up speed until it hit the bottom at 70-75 mph and then reach the next hilltop at my target 25-35 or so mph.

What was very useful about this information is that knowing that pedal position is your "MPG setting," you can do a pretty good job w/o any instrumentation.

Now keep in mind I'm driving 5th gear (top gear) and obviously engine revs never reach more than perhaps 2500 rpm.

I drove an HHR that instantaneous MPG dash readout and it was similar but not the precise relationship shown in the Scion. Of course the HHR was an automatic and no matter what throttle position, on the level it could only do a best of 35 mpg. The Scion could actually exceed 50 mpg on the level but the pedal position was too small to humanly maintain. It was probably equivalent to a 1/4 turn of an idle adjustment screw.
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The irony of all this is that a "smart" cruise control would be a fixed pedal position(!) So I was thinking a Hand Throttle would work.

The issue with design a Cruise Control would be knowing where the hilltop was.

One technique might be to allow speed to drop say 10 mph below the setting without changing throttle position. Once the drop was experienced, slowly increase throttle position until the set speed is achieved. There is nothing so infuriating when the Cruise bludgeons the gas pedal right at a crest.