Why Stuck Throttles Are So Dangerous: Loss Of Vacuum

Something that hasn't been discussed widely is the role of engine vacuum in the unintended acceleration issue.

The reason that you only have one chance to brake a car which is experiencing a stuck throttle or unintended acceleration is that at wide-open-throttle, the engine is not generating any manifold vacuum.   Without manifold vacuum, on most cars, the hydraulic brake booster will ingest air as the brakes are applied.  Pumping the brakes will fill the booster very quickly.  Without vacuum, the brake pedal will be very hard, and it will require a huge amount of brake pedal force to stop the car.