brakes suck

Sounds like your problem is a vacumm leak or screwed up vacumm lines, in fact i'd say there's a 75% chance that's what it is. I've seen and had this problem before.
 
As others said - look for vacuum leak; or if it has a lot of cam you may not have enough vacuum at idle to operate the brakes.

Get it fixed and be safe. Or keep driving it this way and you'll shortly be in a situation where you'll have to buy another car -- then get one with good brakes. :)