the buttery fly sets the the min. air flow. at Idle.
it is set at the factory.
the tps is then set with the preload mentioned.
http://carfix.stufftoread.com/TPS/TPS-p92.jpg
note top data box , one is feeler gauge 0.008 and the 0.016" go nogo is the procedure.
the purpose of all this is to get the TPS switch to close every single time the throttle is dropped to idle, ( if not the ECU autmatic idle never wakes up, and stays dead , no idle controls)
to do this and not have the idle fail every other time.
they preload it. ( diff. from 0.008 and 0.016)
they place a 8 thou feeler guage in the stop screw, boss juncture. per my photo above.
then adjust the tps, so the switch just barely closes (reading less than 500 ohms)
typ, is 50 ohms. (need resistance meter , ohm meter to do it)
then you lock the screw down on the TPS base.
then you insert the 0.016 feeler gauge in the same point and make sure the
switch goes to infinity.
(TPS is UNPLUGGEd, during all adjustments of TPS)
if the switch fails to open,at 16 thou, then you set the tsp wrong at step 1, you over corrected.
if you set the tps to open too far in the throttle angle , a flat spot will happen
in the transistion to off idle. ( that is because you might be exiting Idle at 2000 rpm and that would be bad, "IAC hunting results")
now, since you modified the idle stop screw, you now have to do 2 things at once.
not easy.
set the idle, to the proper 800 rpm with this stop screw , HOT.
while keeping the TPS switch closed.
The duty cycle set up does that. setting the duty cycle , gets the IAC valve in the
center of its range.
so it can lower or increase idle as the need arises.
You could follow this path:
1: short the TPS switch pins, some way. (perm. idle)
2: set idle hot. 800rpm , accessories off.
3; set Duty cycle per book.
4: calibrate TPS switch as shown above and above link.
5 : test IDLE by , throwing on head lights, fan, defrost (not A/C).
if idle holds at 800, then iAC idle controls are working. Trumpets!
6: turn on A/C note 1000 RPM.
hope that clears up an complex subject.