idle surge when brakes applied

[Campbell]

Hi, is it normal for the engine to surge a couple hundred rpm when the brakes applied and released at idle? Its a A2 (1987) scirocco. I'm wondering if the vacuum booster is bad - have changed vacuum lines. Thx

[Matt93SE]

If it's a short-term surge, that sounds iffy but not too bad. If the idle moves and stays while you're on the brakes, then I'd suspect a bad booster.

another way to check is to stick a vacuum pump & gauge on the booster. Try to pull a vacuum on it and see if it bleeds down with time.

[Flyinglizard]

Yes, it will move a little RPM.
Check the O ring on tha back of the MC. It needs one to seal, not many MC come with, and it is easy to leave out.
MM