Mike,
   Before I start "experimenting" with stuff like the AFM I try to make some
notes as to where all the settings are before I change them. That way I can
return to the starting position incase I get "wrapped around the axle". For
the idle bypass screw ; insert the Allen wrench and notice where the short
arm is pointing, say twelve O'clock. Then count the turns it takes to bottom
out and write that number down in a safe place. Then back it out the same
number of turns and it should be in the same place.
   You can also adjust the spring tension on the vane. Clockwise tightens
the spring and leans out the mixture. I think of it as a coarse adjustment
and the bypass screw as fine tuning.
    You can benchmark the spring position by either scratching the black,
plastic wheel or counting the number of clicks, counterclockwise, it takes
to lift the vane off of the stop. I would be interested in that number.
   I have successfully used your method  (before going to Emissions Testing)
many times. The last time though, I think the O2 sensor was bad. This caused
me to loosen the spring too much, which coincidentally, gave similar
symptoms. The truck had a terrible hesitation off of idle.

If all else fails, a new catalytic converter always results in Emission
numbers in the single digits. YMMV.

Ken Lewis
http://neksiwel.20m.com/