And we are back to the CEL being on and not knowing why…
The Booster can be tested for that theory by hitting the brake while in park and seeing if it revs the engine, then clamp off the booster vacuum hose or disconnect it and plug it and see if it still does it…
But a simple booster test might give you some insight also…
With the engine off press the pedal several times until you can feel that it’s firm . That indicates that any vacuum in the booster has been discharged. With your foot still on the brake pedal, start the engine with foot still on the brake pedal. Notice if the pedal begins to get soft and drop under your foot.