IAC is definitely 12 volt, if you have a scope, you can confirm this, however GM schematics imply it as well as Ludis's document all imply that the IAC is driven directly off of system voltage.
Directly off ECM system voltage?
1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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