2003 bmw z4 idle problem when brake pedal is pressed..

i have a 2003 bmw z4 2.5l motor.. the idle rises when i push the break pedal.. i thought it might be the brake booster so i disconnected the vacuum hose to it and it still does it.. i checked it for leak at the intake manifold and found nothing. if someone has come across this problem please any information would be much appreciated...thank you

only thing i can think is from old cars.....some had a vaccum switch on the brake pedal and although rare cases when stepping on the pedal you make a bad ground good. if the vaccum hose to the booster is disconnected and plugged AND the pedal still changes the idle i would look for some type of vaccum controll on the pedal. imho