If it goes away once it's heated up it's more likely the FITV (fast idle thermal valve).

You can test the IACV by unplugging it from the back of the intake manifold.... I think the idle should drop/car die. if not then the iacv is bad...

if it does then move on to checking the FITV... remove the FITV and cover the top part with something that won't melt/leak and re-install... hope it works...