I have a 1997 4Runner its has low miles. It idles fine at lower altitude which is where I normally drive it. It idles at 2000 RPM at high altitudes. It seems like the dashpot is extended holding the idle high. it is bad and needs to be replaced? or can it be adjusted? It has never been adjusted the yellow Loctite is still on the screw thread/nut.

 

I've had an issue with my dashpot having a split in the rubber boot and it allowed dirt to get inside thus keeping my throttle open a little bit more than it should be. I took off my dahspot a year ago and I have not had a problem yet. The purpose of it is to keep the throttle from snapping back when you let off which can lead to backfiring or harsh deceleration. I would try to back it off a little and if that doesn't help then i'd pull it off and see if it helps your high idle issue.

 

Your location info is not showing under your screen name so we have no idea where you are or the altitude(s) you are working at. Pictures would be helpful too.