Im trying to help my father out with his 996. He decided to carefully wash the engine bay with water and mild soap a few weeks ago. Since then he has a horrible smell coming through the vents once he starts the car up. It disappears after a few minutes but is very strong at first.

I was thinking it could be the cabin filter but how could that have gotten wet with it in the front of the car?

 

What is the smell? If he used mild soap, it should smell like soap right? Did he wash the car also? Mildew? Check the carpet, maybe it is wet and mildewed because the drains in the front are clogged and the interior got wet.

Open the front boot lid and remove the cowling near the windshield. Maybe a squirrel or something got in there or just a blockage of the drains.

 

musty, mildew like smell, like a wet filter. the smell comes through the vents when the air is turned on

 

I don't know how the cabin air filter could have gotten wet from washing the engine compartment, but it sure sounds like mold in the filter. It won't cost much to change out the cabin air filter (I'd recommend a carbon impregnated filter), and it's an easy DIY, to see if that solves the problem.

 

Check the carpet under the seats. Is it wet? Smell the mildew more?

Likely the water drains are clogged and/or cabin filter needs to be replaced.

Water drain locations:

http://www.renntech.org/forums/topic...230#entry51230

Cabin filter change instructions:

http://www.renntech.org/forums/tutor...-instructions/

 

I had a heater core leak and it smelled bad thru the vents. Fogged up windows as well. I replaced it and smell eventually cleared up.