Why does the throttle rise when stepping on the brake?
2 Answers
This fault phenomenon may be caused by damage to the engine's vacuum tube. Detailed analysis is as follows: 1. Vacuum brake booster: There is a vacuum brake booster in the braking system, and the vacuum level of this brake vacuum booster is provided by the engine. Therefore, when stepping on the brake, the RPM may increase, which is likely due to a damaged vacuum tube, causing incorrect engine vacuum levels and thus changes in RPM. It is recommended to check this component as soon as possible. 2. Brake booster: During the braking process, it controls the vacuum entering the booster, causing the diaphragm to move, and through a linkage device, uses the pushrod on the diaphragm to assist the driver in stepping on and pushing the brake pedal, thereby amplifying the force applied by the driver.
I last encountered this situation in my own car. When I stepped on the brake, the engine RPM suddenly surged, which gave me quite a scare. Later, after inspection, it turned out to be a vacuum booster leak—the aging vacuum tube had developed a small crack. Every time I braked, more air was sucked in, causing the RPM to rise instead of drop. The mechanic replaced the tube, and the problem was gone. This issue is common in older vehicles, especially those over ten years old, where aging components are the main culprit. If you keep driving like this, it could increase fuel consumption or even damage other systems, so I recommend getting it checked at a professional shop ASAP—don’t try to fix it yourself, as it’s unsafe. During regular maintenance, pay extra attention to these rubber hoses—prevention is key.
