When the vents are closed with the AC on, I can still smell exhaust coming through the vents from other vehicles (especially trucks and diesel vehicles) in front of me when stopped in traffic. It gets so bad that I sometimes turn the AC off when I'm stopped behind vehicles. If the vents are closed, I shouldn't be smelling anything from outside. I can also smell grass being cut outside while driving with the windows closed, vents closed, and AC on. I can live with this annoying problem and didn't want to spend the money to have it investigated and repaired. The repair sounds like it would be expensive.