As of last week I started smelling a what I think is exhaust fumes coming out of the air vents with the heater on low. It only occurs when I have the hvac unit set to pull air from outside. This made me think that the problem is under the hood, somewhere between the engine exhaust manifolds and the downpipe as how else would exhaust fumes get sucked into my car by the HVAC system?

This weekend I went and thoroughly checked my exhaust for a leak w/some soapy water and a by pulsing the throttle. I thought I found a leak coming from the turbo but when I went to check it again, I didn't see any bubbles. What I saw before could have just been a result of the hot turbo.

So at this point, I have a feeling the problem is Not the exhaust. I could be wrong. I am wondering if there is anything else that could cause that problem.

I might check for the problem stated in this thread, but the smell is more like exhaust fumes than raw fuel. Additionally, it only goes down to the low 30's at night an d the problem is evident no matter what the tempreature is outside.

Thanks in advance for your help!