I've been down this road with the stock TB and making
the hole smaller than factory-stock does not help - it
hurts, by making the IAC "wind up" trying to get air that
Look to low-end airflow accuracy -> mixture for your
stability problems. Tuning to stoich on the wideband is
not going to be real accurate with a big cam. You have
to play with it, and see what indicated AFR idles best.
And then keep closed loop from ruining it, if you're
trying to keep closed loop operation.