How I finally got mold out of a stored car — steps that actually worked

Dealing with a moldy car interior is the worst, sorry your sister is going through it. I fought this in my wife's old Corolla after it sat behind our garage for a summer under a tree cover. The seat bolsters and the passenger floorboard got the worst of it, and I learned the hard way that the visible patch is only half the problem. Pull the floor mats and check their undersides, and if the carpet feels damp anywhere, peel it back and look at the padding and the spare tire well. Ours was holding moisture in the foam under the driver side carpet long after the surface looked dry, and the smell kept coming back until I got a box fan blowing into the cabin for two full days. On the cleaning side, I skipped the spray route and rented one of those little portable carpet extractors from the hardware store, about forty bucks for the weekend. Doing a proper wet pass and then extracting as much liquid as possible worked way better than misting and blotting for me, and it kept the drying time short. I did follow the same idea on the headliner though, just a barely damp cloth there, since getting headliner fabric too wet makes the glue let go and it sags forever after.

One thing that surprised me was how long the musty smell lingered even after everything looked clean. I left an open bag of activated charcoal under each seat for a week and that finally killed the last of it.

My sister's car had this same thing after a winter in a shed, though hers was mostly on cloth seats and door pockets. I helped her wipe it down with soapy water first and that alone got a lot of the fuzzy stuff off before we did anything else. The seats were fine but the smell hung around in the little vents on the dash for weeks.

Does any of this stuff work diffrent if the seats are leather instead of cloth? Hers are leather and I don't want to spray the wrong thing on them.

Leather changes things a bit, yeah. Had a mildew situation on the leather seats of an old wagon I bought at auction, and the vinegar spray route people are describing here can dry leather out and leave it cloudy. What saved mine was a dedicated leather cleaner first, then going back over everything with a conditioner once it was totally dry. The mold had left faint dark spots where it sat longest, and conditioning after cleaning faded those a lot. Wipe with a damp microfiber, don't scrub hard, and keep the car aired out after. Leather hides less than fabric does but it punishes you for soaking it.

One spot that keeps getting skipped here is the rubber weatherstripping around the doors and trunk, which is exactly where mine came back from twice before I figured it out. Mold loves sitting in those little creases, and wiping the seals with a damp microfiber and a bit of soap gets the fuzz off without touching the fabric at all. Also worth checking that the evaporator drain under the car is actually dripping when the AC runs, because a clogged drain will keep re-wetting the passenger side carpet and undo everything you cleaned. If the smell returns within a week of a thorough job, that drain line is my first suspect.