[Phantom]

Just start with the simple things first clean all the hard surfaces one or two times if you are still getting brown residue on your rag let it dry and go at it again.

If it took more than 2 times to get the dash and windows clean I would start on the soft surfaces by using a carpet cleaner with upholstery attachment. If you can remove any of the seats easily I would do that to make it easier. Do the first wash with warm water this will remove the looser surface dirt then when finished start over using soap.

I'm not sure what I would do about the head liner other than using fabreze.

Replace the cabin air filter and clean the passages under it, also clean the vents and as far down the vent as you can. I hope that the last owner did not smoke with the air recirculating in the car. If they did you might want to check into how to clean the condenser core. I would try the other steps before trying to clean the air system any further than you can easily get with a rag.

Also on hot days leave the windows popped so it can air out.