1500 rpms sounds about where it idles with the pcv or brake booster hose disconnected. Id check for a vac leak due to a loose tube. There should be three vac tubes connected to the intake manifold directly, and one going into the TB near the MAP sensor. Also check the "tree" on the passenger side up to the pcm and all the other little runs for breakage that can cause a leak.

Sure sounds like a tube disconnection to me. Ill bet the IAC pintle is full closed and its still keeling high.

Only other thing I can think to check is to make sure thee is no obstruction to the throttle plates closing completely. They should be almost parallel to the ground at idle with only a very small tilt toward the rear.