458 brake pedal goes stiff after engine start but ok afterwards

(cross posted to 458 sub-forum)

Hey guys,

I took the car out to PCH this weekend and had the brakes act weird at least twice upon vehicle startup. The brake pedal felt fine and had some travel when I pressed on the brakes before pressing the engine start button (engine is off). Once the engine is running, when I press the brake pedal again to engage reverse gear, the pedal is stiff with very little travel (as if no vacuum assist available). I backed the car slowly a few feet and when I pressed on the brake pedal, it felt fine and had normal brake travel and feel. This happened at least twice when starting the car and reversing out of the parking spot. It did not occur at speed or while moving. I tried to see if I could get the dead brake pedal when stopped at a stoplight and depressed the brake pedal off and on repeatedly and quickly. I didn’t get a dead stiff pedal but did detect slight difference in pedal firmness and maybe travel-I figured maybe this was due to quick repeated brake presses and vacuum wasn’t building up quickly enough in between brake presses. Has anyone seen this on their car?

There’s a vacuum hose assembly that is shaped like a “Y” that connects into each intake manifold and then joins together and plugs into another main line that runs along the bottom of the car towards the front. This hose assembly looks to have two check valves, one for each manifold. I’m wondering if it’s possible to disconnect at one manifold and apply vacuum and check for leaks and repeat for the other side? I am not sure if the hose assembly is accessible and can be replaced. The other area could be brake booster underneath the windshield wipers, but I am not sure why or how I am getting a hard brake pedal after the engine first starts, but seems fine afterwards.

Any help would be appreciated!

Ant