I have a mildew smell coming from the inside of my car. Keep in mind this car has never been in the rain but has sat indoors for a very long time before driving.
What car do you have? Could be A/C evaporator box with a clogged drain tube, or if its a 308/328, check the lower R/H side of the trunk below the antenna and see if water got in there from washing the car or something.
Auto parts places sell stuff you can spray on the carpet which are supposed to neutralize smells that are imbedded in them, not just cover the smell up. I'm not sure how well they work. Birdman
if the above solutions aren't to your liking, buy a bag of charcoal and put some in a big open container. place it on the floor, put on the roof, raise the windows and leave it sit for a spell. cat litter in an open container works as well. most likely the funk is coming from the carpets or mats if you have them. ducting in the dash can harbor odor. most likely it's the carpet.
Believe it or not, that Fabreez stuff does work. You need to check the air conditioner hose that is in the passenger compartment. Either it is plugged or no longer draining to the outside. If you don't fix it, the smell will always come back (or never leave, really). Good luck. Alberto
