As William said, that rubber tube supplies cooling air from the air intake chamber to the blower motor. If your car is like my '95, you have a hard rubber insulating cover over the blower motor - these are available from the dealer for about $10. I had to replace mine. The entire heater/AC box on the engine side of the car is also covered with this hard rubber stuff. When I had my engine out, I replaced my broken cover with a good one from a junkyard. As I recall, it wasn't all that easy to change even with the engine out! The motor cover is easy to change. If that is the end that is crumbling, just install a new cover and plug it back in. If the other end (on the chamber) has crumbled away, you might try to use something like silicone RTV to patch it back up enough to re-install the tube. I'll try to get you a pic.