I recommend replacing the glow plugs with a good quality plug like the Bosch Durotherm, cheap plugs can and will stick in the heads and break off the next time you try to get them out causing you to have to remove the head.
IDM (Injector Driver Module) basically a box that makes around 110 volts DC power to fire the injectors, its unlikely that this is your problem because when it goes you usually loose everything but I have heard of at least 1 case where it went bad and he still had one side.
The plug in the valve cover gasket is know for problems, there is a lot of juice flowing through there when the plugs are on and it tends to melt things.