Periodic backfire into intake on NG engine

[David]

Patient is my 1987 Coupe GT 2.3. This has hppened 2 or 3 times. I will be cranking to start her, I hear a bang or pop and she wont start or runs terribly. Upon inspection, I find that a vacuum hose has popped off or been "popped" by excessive pressure. The first time, I assume ti was jsut loose to begin with and had popped loose. But the pop/bag noise makes me wonder if it might be a back-fire into the intake. So, any thoughts on what would caudse her to back-fire into the intake? Doesn't happen often, but is really inconvenient when it happens and disables the car just when I need her most...

Dave
1987 CGT 2.3
SE VA