I believe the hose comes off the back of the plenum and goes right over to the brake booster. May need to remove the intake hose to completely get to it.

a friends hyundai (sp) had shifting problems...turned out to be the crankshaft sensor.

failed twice on him

It sounds like the pcm and gone into 'limp home' mode, go get it scanned for codes free at Autozone, Partsamerica, Napa, Advanceauto. Once you have the codes we can get you a better idea if whats wrong. Also, loss of vaccum to the brake booster usually results in a hard pedal, not a soft one. Tha sounds more like air or water got in to me.

Most likely it is still under warranty and the repairs will cost you nothing but your time without a car. Take it to the dealer.

How many miles are on it?

EDIT for stupid mistake.