sounds like you have a bad(big vacuum) leak... there should be a hose going to the brake booster(the metal can behind the master cylinder.... kinda big vacuum hose(maybe 1/2 or so)..... pull it off and put your thumb over the end of the hose where it goes (or used to go) to the brake booster..
you should feel a pretty good pull of vacuum on your thumb.. if not then you found the problem.... travel along and see if you can find any loose hoses???? and a vacuum leak will give you a bad ride also, loos of power and the engine hunting for an idle, high speed idle, etc????
the loose hose you found on the area under the battery might be the hose that you need to attach to the brake booster or somewhere along the line to the brake booster??
hope this helps.,... been there with other cars, so talking from experience....
