Thanks to Paul Nimz
The correct (and only way) to set your idle in the V8 SHO is to drain the
brain, start the car and let it idle in park until it settles down (20 seconds
or so), move the gear selector to drive and wait for it to learn, then turn on
MAX A/C when still in drive and let it learn, then shift it back to park with
the A/C still on and after a few seconds it should be all done.
If you mess with the throttle stop at all it is a losing battle. All you can do is make it idle too fast. The correct way to set the throttle stop is to set the idle stop clearance to 2mm and then turn the screw in an additional half turn.
Followed by the idle learning regime listed above.