I'm assuming you are using a default Plane, i.e. the 737-800? I have posyed this before, but this should help you. Go into your Key Command Tab, find Shift + E for opening and closing doors. Change this to any single Key (that's not already in use). So now when you want a particular door opened or closed just press your assigned Single Key + 2, 3 etc. FSX has a timming issue with a three key command, and anyway you find a two key command much easier.