It's rather ironic that the AFM started to play up just after plugs were installed. Maybe the burnt fuel reversing through the intake did have some affect on the AFM. I mean it just seems to be to bigger coincidence, and why did they choose range 7 plugs for stock car, they must have pulled them out of a hat.
As for the door, $600 is wrought. It really does show that doing your own work is the best way to go.