I've found you can have that hanging idle if you got two things outta
whack that kinda work together.
The tb blade stop screw
and
The tb air bleed screw
Basically ... you wanna have the stop screw just barely holding the blade
open to keep it from sticking on the side of the tb bore.
I have seen the bleed screw being out too much will also cause this issue
These two next things can greatly help you obtain a stable idle
You also wanna up your tb airflow value scalar a bit
and
Your ISC Neutral Idle Airflow function values as well
There are specific procedures for obtaining the best values for that
scalar and those function points
Look here in tech and tuning for info about the methods
and
I think I got some info on my site for the details as well
however
If you wanna shoot from the hip
You could add about 10% to each function cell
and
About 70% to that scalar
It should get you closer
Grady