Power Brake Booster Check Valve
WARNING: This page is about a different car, the 2004 Ford Thunderbird. However, it is still accessible from the selected car via links, so may be relevant.
Start and run engine for at least 10 seconds. Operate brake pedal to check for power assist. Disconnect vacuum booster hose from power brake booster. DO NOT remove check valve. There should be enough vacuum retained in power brake booster for at least one more power-assisted brake operation.