Eratic Idle When On Brake?

[Nd4SpdSe]

I know nvrsrndr ust posted something similar (and he lives not too far either, so i'm guessing thats its weather related)but when my car gets warmed up, about 10 minutes of driving, whenever i press on the brake pedal when the engine is idling, my idle bounces contantly between 1500rpm and 500rpm. but only when i press the brake pedal. I can put it on neutral/press in the clutch and apply the hanbrake and release the brake and it stops, but as soon as i press the brake, it starts again. It continues on the whole trip until i shut off the car and let it cool down.<p>I ahvent experiences anything odd while driving, jsut when im on the brake

[IanL]

Brake = Vacuum servo
Idle fluctuation = vacuum line problem?<p>Common factor = vacuum pipes?

[tehbrookzorz]

IAC valve adjusted too far open to compensate.

[mazdamx3freak]

or you have no check valuve on you brake booster

[hgallegos915]

ditto on the no brake check valve. I dont have one and it does this lol

[mx3autozam]

ya but the check valve won't cause this. It just holds vacumn in the line for when you are in higher revs were there is no vacumn so your power brakes work. But regardless get one!