Strange issue with Engine and Brakes

I was taking my daughter out for a lesson in our '93 Lumina APV 3.8. When she turned the ignition on to start the car there was a load bang from under the hood, smoke poured out and the engine died. There was an electrical fire smell.
I cleared the smoke and tried the engine again, it would start but not idle without holding some revs on with the accelerator.
The engine was accompanied by a high pitched rattling noise, and there was no brake pressure whatsoever, i could however get the car into drive and reverse and drive it after a fashion, though it was lumpy and rev limited.
What on earth could have 'blown' and affected the brakes? The smoke was quite substantial at the time.

Many thanks in advance for your time.

Does the van have vacuum assist or hydro-boost brakes? If they are vacuum assist, check the vacuum line to the brake booster and the check valve. Leaking vacuum would require a little throttle to keep the engine running and rough running.

INdeed, you probably had a backfire, a minor event, for unknown reason (to be investigated later if it perdures), but it obviously blew a vacuum line out, whick inhibits the brake booster and provides poor idle; you will probably notice none of the heater/AC control will work to direct air where you would want it; cruise control will also be inoperative because it works from vacuum. THe main vacuum hose is between the intake manifold and power brake booster. Check for this.

Blue Bowtie and LMP,

Thank you very much for your responses, i will check the hoses when i get back from work today, that sounds very much like the answer to my issue!

Will let you know once it is sorted.

I think the reason i had the backfire was due to my daughter turning the ignition on then off quickly (she hasn't quite got the hang of starting just yet)

Happy to say this issue is now fixed!! It was so easy, just re-attach a vacuum hose and everything is sorted!
Thank you once again LMP and Blue Bowtie for your help in this matter!!