What is the reason for sudden high idle speed when stepping on the brake?
4 Answers
The reason for sudden high idle speed when stepping on the brake is that the transmission downshifts, causing a momentary increase in torque, which is a normal phenomenon. The braking system consists of a vacuum booster pump, master brake cylinder, wheel brake cylinder, brake pads, and brake discs. The brake has the function of reducing vehicle speed, and the precautions for its use are as follows: 1. Slow down: Brake gently when following another vehicle. 2. Rainy days: Use emergency braking cautiously on rainy days. 3. Braking: Avoid using emergency braking on slopes and curves. The solutions for brake failure are as follows: 1. Pedal: Release the accelerator pedal. 2. Gear: Shift to manual mode and manually downshift from high gear to low gear. 3. Handbrake: When pulling the handbrake, press the release button and pull the handbrake continuously, but do not pull it to the locked position. 4. Parking gear: Shift into park after the vehicle comes to a stop.
Over the years of driving, I've encountered several instances where the idle speed suddenly increases when braking. The most common cause is a leak in the brake vacuum booster system. When you press the brake and need assistance, air leaks into the system, causing the engine to draw in more air, which spikes the idle speed. Check if the vacuum hoses are aged or loose, especially at the connection to the intake manifold. Ignoring this issue can lead to reduced brake assistance, affecting braking performance. Similar problems may also occur during cold starts. It's advisable to have a professional shop check the vacuum level and booster seal integrity as soon as possible to ensure driving safety.
My old car had this exact issue - the tachometer would spike when I hit the brakes. The main culprit was vacuum leakage in the brake booster system, like cracked hoses or loose fittings, causing the engine to draw extra air and raise idle speed. It could also be an erroneous response from the engine control unit, requiring computer diagnostics. Don't attempt DIY fixes carelessly, get it inspected promptly to avoid brake failure risks. While at it, have them check for carbon buildup in the idle control valve, and develop regular maintenance habits.
A sudden increase in idle speed when stepping on the brake is mostly caused by a vacuum leak. The system fails to compensate properly when the engine load changes, resulting in increased RPM. Simply check the vacuum booster and hose seals. If there's no improvement, seek professional repair to prevent the brakes from becoming stiff.
