A true cold air box will not lean the AFR it will richen it up a bit since the outside air is much cooler, thus IAT reports lower temps, plus the intake manifold is now getting that colder air.

With the cold air box, larger injectors and a proper PCM calibration my '99 C5 has gone from 435 HP at the flywheel to over 500 and torque has gone from 350 to around 400 ft/lbs, so clearly the changes are a positive to overall performance and in the end the numbers tell the story better then reason why or why not injectors are needed or not.