Black plug in back of blower

[Humboldt Cobra]

I was shifting from 3rd to 4th at wide open throttle and my car hesitated
again. It started running real rough so I pulled over and found a black
plug had come off the the back of the blower. I plugged it back on and the car started running fine. Has this happened to anyone? And why?

 

[03Saleen]

I was shifting from 3rd to 4th at wide open throttle and my car hesitated
again. It started running real rough so I pulled over and found a black
plug had come off the the back of the blower. I plugged it back on and the car started running fine. Has this happened to anyone? And why?

My vacume hose blew off of the back of my blower and the car ran ruff and died, scared the SHIT out of me.