2 years ago, after a massive weekend of rain, an ambulance fleet we service had 3 IDMs go down on the same weekend. They then decided to replace the IDMs on the rest of the fleet (about 10), and let us keep the old ones... nice, eh? So everybody now has a tester...
Now that I've got that out of the way, an IDM can cause that. Alot of the time, a visual inspection of the IDM, along with a good sniff can give an idea of the condition it is in.