Hey im new to this forum, and my friend is selling his 99 Millenia S. I want to buy it but i also dont wanna put 2 grand into it as soon as i get it. I was told the odor coming through the vents was the catalytic converter. To me the odor smells like gas fumes and the mechanic checked the whole fuel system andsaid there were no leaks.At once the check engine light was on, and we took it to autozone to get the code checked, but i don't remember what the code was, because it's not my car. We had the alternator replaced recently and the check engine light is now gone but the odor is still present when you turn the air on. Is this problem really the cat, and if so why hasen't the check engine light come back on. Also the car really hasen't been getting driven since the alternator change, so im thinkin thats why it hasen't come back on.

 

It could be mold on the evaporator. There is always moisture in the evap casing so any debris that comes in the vent collects and creates mold. Get a bottle of mold killing bathroom cleaner,turn the fan on with outside air vent on. Spray it in the grille just under the windshield outside so it can be picked up by the fan and coat the evap core. If it is mold the smell will go away. If it is a gas leak it will usually only leak on a cold engine so looking for a fuel leak on a hot engine will usually not result in success.