Besides the loose gas cap, you may have switch malfunction on the secondary blower for the emmissions. I had the same problem awhile back. I first called the 1-800 number, who suggested the gas cap then told me to return the car to the dealer (they were great on the phone, even called me later to make sure that I made it to work). The service guys knew all about it and had the switch on-hand since it has been happening frequently. If you search the site, you should find additional information on this malfunction as some folks bought the part and fixed it while the dealership took about 1 hour.