get a product called 1z EINSZETT Klima-cleaner (found online) or possibly some other ho-hum brand found at your local auto parts store. It is a (sometimes foaming) liquid that you put into your evaporator drain tube (or sometimes the center vents w/ floor vents closed!) and it fills the evap/HVAC box and kills germs/bacteria then disolves and drains out the tube again after 15-20 minutes. These are generally $15-$20 and work wonders (before you take things apart!).
In my 2005 TL, if you pull back the carpet on the passenger side near the center (left foot if you are sitting on passenger side), you will see a black tube. Not the wiring tube conduit thingy, but a black tube you can squeeze. It leaves the cabin through a hole in the floor held/sealed by a rubber grommet. You can use the cleaner from under your car, or from the inside, pull the tube/grommet out of the floor and it may be easier to fit in the tube to apply the cleaner (just use caution and have a rag handy, and put right back into the floor hole to drain... I didn't have any probs though).
If continued search for stank is needed:
And, as mentioned, replace cabin filter. If necessary (I wanted to check for rodent droppings and vacuum out if necessary) it is easy to pull the blower motor- 3 phillips screws and it pops out. May check under cowl/fresh air intake for debris too. Center vent and drivers vent on 05 TL pop out to clean if necessary, passenger side there is a screw under silver trim.