Well being in canada I have never actually seen a 3.0 v6 in a truck before let alone examined the throttle body. But from previous mitsubishis I have owned with a galant 4G63 in mind that had a crazy idle problem. It surged between idle and about 1400 to 1500 rpm.

Now this throttle body had I IAC which might actually be the same as a montero a well as what they call a wax pellit high idle. there was two coolant lines that went to the throttle body which would close a auxillary air valve as it was warmed by coolant much like how a thermostat works, and like a thermostat they can fail open giving you high idle all the time!!

Not sure if this applies to the montero but its a idea.