I have a 2002 XLT Explorer and the outside air is coming in with all the vents closed. The a/c works and the heat works. When driving I get the bad fumes and exhaust from cars and trucks on the road. It started about a month ago and I also noticed that when I open the glove box (when driving) the air is coming in through it. I have really bad headaches by the time I get to my destination. Any ideas would be appreciated!

Questions: Should the outside air be coming in if all the vents are closed?
When I do turn on the A/C, it used to only recirculate the inside air, but this is no longer the case, there are strong odors from the other cars on the road.