Pipe between the air filter and throttle body

Servo is at the bulkhead, follow plastic hose to it from inlet manifold, if you can, disconnect the pipe from servo, block it off and start the car to see if it improves (don't drive it..no brakes..) if it improves, the servo itself is leaking. Very rare on modern cars but worth checking.

Also any breather hoses/vac hoses around the inlet.

I don't see many of these cars day to day, so not aware of any common causes for this.