I'd love to see some documentation regarding the link between the Econ button and the actual A/F ratio.

Here's what the '08 FEH Owners manual has to say: (2nd edition, page 43)

12. ECON: Press to activate/deactivate economy air conditioning
operation. ECON mode may provide improved fuel economy by
preventing the gasoline engine from running for the sole purpose of
providing A/C. When the gas engine turns off, the A/C compressor does
not operate to cool the cabin and comfort may be reduced. In ECON
mode, A/C operates as normal when the gasoline engine is running. To
prioritize cooling comfort over fuel economy, deactivate ECON. ECON
can not be selected in (defrost) or (floor/defrost).

 

In the 06s the econ button is the A/C switch. Unless it is in the "Max" position the engine cycles on & off normally.

With regard to air-fuel ratio: I don't know if there is a link in the software, I'll see what I can find. My earlier point is just that the chemistry of the gasoline engine offers a best power and a best economy air/fuel ratio. I'll see what I can find as to whether that's part of Ford's implementation.