Hi, I own a 2000 Bonneville SLE. And most recently ive noticed that occasionally when I am idling at a light I smell a light odor coming from my AC vents. When I opened the hood i noticed that it was the same odor hovering around the engine. In addition I noticed that occasionally at night, there would be vapor coming out from front end of the hood nearest to the driver side. I took it into the dealer, and they said they could not smell anything when they ran it for 15 minutes. They said all the lines were fine, so Im not really sure what else it could be. Any thoughts?

Try changing out the cabin filter to start, you might have mildew on your heat exchanger that is giving you the funky smell. Pita to change out or get at to clean but start with the filter first.

Sure you ain't leaking something, and you only can tell when you sitting?