I've been trying to troubleshoot an exhaust/gas smell coming through the heat/AC ducts on my Audi A4 1.8T for a while. I can only smell it when the car is at idle, at a stop, with the climate control fan on and not set to recirculate.

I am starting to suspect a turbo leak or some other sort of turbo failure.

Since the car does not have a turbo gauge and I have had this problem since owning it, I can not say if the turbo is functioning or not.

I know some turbos cause a "woosh" sound when boost is built. Should this be the case with the A4?

Also, should the feeling of boost be clearly noticeable when accelerating? I don't feel a "kick" after a turbo lag. I figured this vehicle's turbo may be less significant than some others.

Lastly, would an intake boost leak cause exhaust/gas fumes to leak under the hood or would the smell be more indicative of a different problem?

Thanks for any help,

David