[CarefreeAZ]

Have you looked into changing the "cabin" air filter? anda::hungover:

Well, I've done it once and there is a nice DIY post on Fiesta Faction from some years back. It took me 30+ minutes and I suggest going to a few yoga classes before attempting this work. As I have to also replace the fan resistor located nearby, I will be changing out my cabin filter again this Spring.
(UPDATE)
See here:
http://www.fiestafaction.com/forums/fiesta-service-bay/33596-found-cabin-air-filter-4.html