I had a similar issue but a different mod.
Pre-99 GC8's IACV gets in the way of later model TMIC's
Answer I got was:
If the IACV is removed you can increase the idle slightly and it will be fine to drive.
What it wont do is adjust the idle when off throttle load is put on the engine, i.e. aircon, turning the wheels while stationary.
In these circumstances the car may stall or suffer a drop in idle speed.

I would expect your PowerFC is capable of reading the signal form a later IACV anyway.

*Disclaimer: This was in relation to a 1998.
This was from a decent work shop but was a number of years ago so my recollection of the conversation may be off.