Hi MarPac,
Disconnecting the IAC valve on an engine at normal temp should cause the RPM's to drop slightly (to around 500 RMP's at idle), so I think you definitely have a problem.
You didn't post what year is your windstar, but I would make sure the gasket for the IAC and throttle body are OK and the bolts are tight.
If I remember correctly the manual specs a resistance of 8-13 ohms; however such reading does not ensures the IAC is ok and the even manual says so.
Oscar.