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.