Black Dog with Patrick Swayze, has 3 black notchbacks chassing a semi truck
at the start of the movie I think. http://www.imcdb.org/vehicle_2141-Ford-Mustang-1993.html
I restored mine about a month ago. To remove them there's one screw under the molding and slide them out, you'll be able to see it with the door open. With what I spend on materials and time spent on filling and wet sanding (that plastic coating is stuck on, I just removed what was loose on the...
About the check valve, did you purchase a generic piece or is it specific to the Mustang,
I got to check mine. I still have codes 41,91 after replacing all rubber vacuum lines.
I have that same housing (T-bird) but swapped electronics from a 94 stang with no problems or you can use any of the electronics that jrichker posted. Remember 4.6 t-birds/cougars use obd 2 electronics (94-95 Stangs obd 1)