backfire

My 92 960 wagon backfired while starting. It blew off all 6 of the intake manifold connection boots, and left the intake manifold itself tilted about 2 inches to the driver's side. Repair at the side of the road took about 2 hours and involved pulling the fuel injection rail, the injectors, and fighting the boots back into place. I plan to replace the boots and clamps. Question is.......why did this happen? Is there a connection to hold the manifold in place, other than the boots? And why the backfire.........that's a first.