Well, since it goes away by tapping the throttle, it's probably not a vacuum 
leak. If the throttle switch and its associated wiring and connections are 
OK, the next step is probably the dang idle controller or idle air valve. 
Perhaps the air valve is sticking? 

The weather has been a bit cooler here in
> Vancouver lately (dew on the windows in the
> morning, ya know) and the Van is idling very
> high on start-up and when it's cold. When it
> warms up it idles at normal speed with occasional
> high idles, cured by blipping the throttle. The
> throttle is not binding and the idle switch is
> good. Only other idea I had was the idle air
> bypass, which I haven't yet checked.
> 
> Before I actually go and get my hands dirty, does
> anyone have any other suggestions?
> 
>