I have a new 2011 Prius 3. (1900 miles)The other day I had my elderly mother waiting in the car for me while I got her some groceries. When I returned the interior smelled like exhaust. (she didn't notice). The ac was off but set to outside air with the fan running. I figured it was because I was parked and maybe sucked in exhaust from another vehicle. However last night I noticed the odor again this time just from regular driving with the ac set to outside air and I could smell it again. I checked the oil filler cap as suggested in a previous post. I smell it more on my clothes when I leave the car than when I'm driving it. weird.