[Raceboy]

Narrow-band lambda is completely useless as a tuning tool for any engine operating range other than tuning idle and/or very light load where lambda values should be at or around stoich (lambda 1.0 = 14.7 on gasoline).

And most 911 engines like a bit richer idle (creates better vacuum), like 14.0 (lambda ~0.95), especially when dealing with hotter cams and/or ITB's.

At WOT the sensor reads just "rich" and does not give any information how rich. Of course, if your lambda sensor reads "lean" and WOT, it means either trouble with the fuel delivery or too rich (rich misfires read lean on lambda) and still, narrowband lambda is useless.

Its only purpose (and what OEM meant it to be) is to correct mixture at idle and low loads reducing pollution.