revs rising

[big tone]

last night after the drags
I noticed that when i applied the breaks the rev revs would rise about 500rpm
it use to only rise about 50 -100 rpm but now it bad
would it be inlines with the booster or somewhere else.

[ECU-MAN]

sounds like the booster could be bypassing. can you hear a long hissing when you press the brakes coming from the booster.

[vinnY]

my brake also has the same habits, brake and it'll raise the revs 2-300rpm on idle
at the lights it'll idle normally at 750rpm while holding on to the brakes
if i pump it a few times it'll rise then drop to normal if i hold it

would a brake master cylinder rebuild fix the problem or does it lie elsewhere?

[big tone]

No Hissing