Why replace idle control valve on a 2002 Highlander?

The Idle control air valve on Highlanders, and other Toyota models, and other makes and models of vehicles, becomes dirty. On my Highlander, the dirty valve caused the vehicle to sometimes fail to idle on its own until it warmed up. My research shows that most of the time these valves don't need to be replaced, they just need to be cleaned. If you can locate yours, and have decent mechanical skills, you can clean it and save the cost the dealer would charge to replace one. If you go to the website for "Tundra Solutions" you can find various posts on the Highlander issue, including my detailed summary of how to remove and clean one on a Highlander.