i've never seen mine work either on high idle. I would like to see the high idle thing work kinda like are ford ambulance. As soon as you put the parking brake on and it was an auto, the engine would automatically go to high idle. I think that's the way it should be regaurdless of temp. Even if it idles up in the summer time it's better for the engine that way and the a/c will tend to work better also. Have the 3 cyl cutout feature set for where the high idle is supposed to work on them now. I'm not saying mine doesn't work, but is was about 24 here this morning and the truck had sat for about 14 hours so i think it should have worked.