Whilst driving a hissing sound can be heard from the brake pedal. Like air escaping. During idling, the revs are higher until the brake pedal is pressed causing the revs to drop to normal.
Hi,
From your description this appears to be a Brake servo issue.
The brakes are assisted by a vacuum created from the draw off the inlet manifold, it gives assistance too the brake pedal pressure by a large tank/cylinder mounted on the Bulkhead/firewall.
I feel that the sound you a hearing is air being draw into the Brake Servo from the foot pedal seal and the reason for fluctuation in the engine is the vacuum from the inlet manifold is being upset.
Attention I suspect should be addressed to the Brake servo/pedal seal or gaitor.
I hope this clarifies your thoughts?
Please remember to rate my effort.
Paul 'W'
Onyer~EDSon(:0) {#><U.K.
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