Mildew killer available in Pep Boys and other fine auto parts stores. They don't always have it in stock. Popular item around here since there is so much AC. After doing this you can prevent this in the future by venting the AC before shutting the car down for the day. When you get about a block from your house, or work, turn the AC to vent and the fan on high. This will blow the water out and help dry the system. Mine has never had this odor. My wife forgets to do this and her AC stinks everytime on start up. Even her 03 Tribute has started to get a little rare....
