At startup the IAC are set at 144, I think that setting can be increased somewhere in the bin. The intake passage will affect only idle quality and you should eliminate every other possible reason before doing it.
Too much and you will never have a good idle again, The individual cylinder trims will get all around and will need a fresh tune from zero. Even GM made different size holes to compensate for the unequal air distribution.
Once I made the mistake to make the holes the same size and the idle was crap with constant surging. Only fine tuning ind cyl trims make it run stable.

Humidity hits the ignition system to the limit, so it will be good to take a look at that first.