My 02 5.4 has 163k miles on it and the idle air control valve had never been cleaned. Lately, it appeared to stumble a bit when I first stop at a light. So, I figured it was time. It is located behind the throttle body on under the upper firewall and is a bit of a pia to get to to remove but I managed. It wasn't that cruddy but I do think cleaning it solved the issue I was having.