1985 Vanagon - How to check brake booster for vacuum leak

[Cpetry7]

Have been hunting down issues with my ‘85 westy stalling out at idle/when braking. Did a smoke test in the engine bay and saw no vacuum leaks. I have confirmed the idle control module, o2 sensor, and air flow meter have been replaced recently to no avail.

Did some testing to how braking impacts idle and can confirm that idling rpms shoot up when applying the brake while in park + I have to apply a small bit of throttle to keep from stalling when braking to stop. I have also noticed a subtle hissing noise in both of those scenarios. This leads me to believe that I may have a vacuum leak in the line that connects to the brake booster.

Is there a way to access that line without pulling the instrument cluster? Has anyone run into this issue and troubleshot before?

[4Gears4Tires]

You could access the line in the engine bay. Look for the yellow ringed check valve on the driver front quadrant.
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'87 Syncro Ferric Oxyhydroxide Superleggera Edition
'85 Westy Sciuridae Domus Edition

[MarkWard]

For testing, disconnect the booster hose from the intake and cap the intake port. Van will still stop with extra leg pressure. See how the engine runs with the booster bypassed.

My hearing is not what it once was. Generally most folks would not “hear” the booster working. There is an O ring seal between the master cylinder and the booster that needs to seal.

Removing the cluster gets quicker the more you do it. I don’t even think about it anymore.

[Cpetry7]

@mark ward - this looks like what you are talking about based on the response from 4gears4tires and what I have seen in the Bentley. Is that correct?

[4Gears4Tires]

Yes, that is it.
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'87 Syncro Ferric Oxyhydroxide Superleggera Edition
'85 Westy Sciuridae Domus Edition