MAF sensors work on a heated wire principal. The wire is heated and then the resistance is checked, then the wire is pulsed to return i to a "known" resistance. The amount of pulses it takes to return that wire to the known or base resistance is reported to the ecm as a Hz signal. Hence the lookup table is referenced in Hz. MAF sensor performance is based on is internal processor, the supply voltage and ground.

As for humidity, if BARO is not reading within 3 of reported actual baro, the air density calc can be off. The humidity flowing over the MAF wire cools the wire, misreporting actual airflow. We are trying to calibrate a sensor table to report a mass of air that happens to include oxygen. Temperature (iat), mass flow(MAF) BARO (key on MAP) reading and engine vacuum (VE) determine the air density being delivered to the cylinder. So the actual humidity is not that big a problem. Its impact the actual combustion process in the chamber not so much the calibration of the engine. The stfts are fast enough to handle the humidity.

The enlarging the idle passages is for allowing the air passages to do their jobs. There is not a "closed loop idle" like there is in a GEN3 engine. If opening the idle bypass does nothing, but opening the throttle blades does, the passages need to be larger. Air in the main intake chamber (non idle passages of intake manifold) can be robbed from cylinder to cylinder if your just gonna open the throttle blades. Cylinder to cylinder fueling will need to be redone either way you choose. If you haven't adjusted the eoit i would visit that as well. Maybe stick a set of injectors in that you have excellent data for, then swap back the the njectors you need for power and adjust the injector data around the idle data from the known injectors.

Chris