i just brought a 07 kia optima and the air stinks when first turned on .It is used and 30,000?
that’s usually caused from leaves or debris that got caught up in the outside vent and got pulled in to the heater box,then this rots,and that’s what causes that too happen,it usually wont clear up on its own,it usually has to be removed,and it can also be old water standing in the heater box and that is caused by a drainage block for the air conditioner,that can be cleared out with a piece of wire ran through the drainage hole to free the drain plug on it,you may want a shop to check this and make sure its not clogged up,if it is it may start coming out in the floor on the passengers side of the vehicle,these are just a few things that it could be good luck.