Sound like you have air air leak in the servo/vacuum path.  Check the hose
connection at the throttle body.  Also the hose for cracks etc.  The valve
you replaced is a one way to stop air being drawn back in to the servo in
the absence of 'suck' from the throttle body.  Unlikely to affect air into
the throttle body unless the housing was split.  The only other route the
air can get into the system is through the servo itself.  You could have a
split diaphram or other servo problem.

You should test the servo as follows.

1) With the engine off, pump the brake pedal through at least 5 to 10 full
strokes till the pedal goes firm and any 'hiss' from the servo is no longer
heard.
2) Whilst pressing on the brake pedal, start the engine.  The brake pedal
should sink underneath your foot.
3) Release the brake pedal.
4) Press the brake pedal firmly and check for any pedal creap/sink over
time.  There should be none.
5) Release the brake pedal
6) Let the engine idle for a few seconds and then switch it off AND DO NOT
touch the brake pedal.
7) Leave asis for 10 to 15 mins
8) Repeat step 1)  This time the servo should hiss on every pedal stroke and
on each stroke the pedal will become firmer and travel less.  Eventually
after 5 or more stokes the hissing will stop and the pedal should be very
firm.

If any of these steps fail, especially 8) then your servo is leaking air and
you should get a second opinion.

Nick /////