Strange exhaust smell in cabin
 

99 Ex.

Not all the time, but maybe 60% of the time when I get off the freeway and come to a stop, I get this exhaust smell in my car. I can't say for sure that its coming from the vents, although it seems like it happens more when I have the climate control set to cold (without the AC on). I know there is no cabin air filter for my car, so what could be causing this smell in the cabin?