Help needed - Idle surging when brake pedal released ?


ej9 and eg6
Jan 15, 2011

As title states, I am having issues with my idle that seems to be directly related to pushing and releasing the brake pedal.
when I turn on the car, its idling at 1500rpm, if I press the brake pedal and keep it held, idle will stay at 1500 but as soon as I release pedal it goes up and down between 1000 to 1500rpm. Eventually it settles back at 1500. Idle before this issue was just under 1000rpm. I have done the following :
bled brakes
checked for vacuum leaks.
checked the check valve/NRV . arrow is facing towards engine and it is only allowing free passage one way
changed brake booster
changed vacuum line hosing form booster to I.M
bled the brakes again
no loss of fluid or any leaks.
The brakes themselves are fine, no spongy feel etc.

I still have the same issue, does anyone have any other suggestions? I think I might rebuild the master cylinder next but if this was the issue would I not see loss of brake fluid and poor brakes?
Also, can the master cylinder be bled by simply bleeding brakes as you would normally at each wheel ?

Any help appreciated. Thanks

Michael Flare

My Final Heaven
Mar 11, 2010
The problem is not brake fluid related like master cylinder, calipers, pedal, etc. The problem is air related because car idle depends on air and the brake booster changes the air intake of engine when it is pressed. I know you checked the vacuum lines but keep looking at other parts of the lines.