what is the brake booster
on 1994 Lexus ES300

Asked by for the 1994 Lexus ES300
It is a round metal case that mounts to the fire wall and the master cylinder mounts to it. It has a diaphragm that uses vacuum to assist the brake pedal pressure allowing it to be applied with less pressure, calling it power brakes.
So can it cause the car not to start
Not that I can think of. Plug the vacuum line going to it and see if it makes a difference.