I might be wrong when saying applying 12 volts to the idle control valve should fully open it because in earlier message you wrote at it's max duty cycle the air valve shuts down the incoming air.
However, when I applied 12 volts to my car's idle control valve the engine rpm increased considerably.
1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.