Were you in the car each time you smelled the smell . . . ?
One thing I would recommend against is using Lemon Pledge to cover up the odor. A friend of mine had some neighbors who managed lose a package of ground beef between the seats in their car, and only found it after it had turned into a horrible, horrible rotting stinking mess. As part of the cleanup, they sprayed a large amount of Lemon Pledge and then left the windows open to air out. Hours later they came out to find a swarm of bees had moved in and taken up residence in the lemon-meat mobile.