Vacuum hissing INSIDE car??

[rlp]

My 03 QX4 R50 4x4 sat in -30 degrees for the first time last nite. OK..now have hissing coming from underneath the dash toward the fire wall.WHEN I step on the brakes it stops. I can touch the brake pedal applying just hand pressure and it stops. I got out of the car, pushed the pedal with my hand and it stopped and stayed stopped. It returns when I drive using the brakes... They work fine and idle is fine, so far.Is this the booster leaking inside the car past the seal and bolts at the brake pedal rod?Or is the diaphragm bad as maybe vacuum should not get to the inside of car anyway?OR could it be loose or some other reason for the leak and hissing???

Any help or experience with hissing under dash at pedal is appreciated...

[Q451990]

Sure sounds like the booster. Not sure how to diagnose it - I assume it would bleed down?

Heath