If the engine runs a little rich, for whatever reason, at first you’ll get an increase in power. MPG will drop sharply before it’s rich enough to reduce performance.
I agree it would probably have better cold start idle/drivability bc of the fuel enrichment. But would someone (especially your average cellphone talking/lunch eating driver) really notice a power increase at very light throttle openings?
If the AFR went from say 14.7 to 12.5 (which anything below 12.5 would just load the plugs) at idle, I would imagine the only thing they might notice would be the mpg dropoff.
Rarely is there much of a power reduction (even at full throttle) from say leaning AFR from 12.5 to about 13.5. Usually its only about 2 percent on a dyno.
I bet the only way they would catch it would be walking behind it and tearing up the mucous membranes.
Kind of hard to test this much. While I can adjust AFR of my carb in my camaro to just about anything I want, I can’t control it at all rpms. And most EFI motors you can’t get that adjustment period. Certainly not closed loop.