What is the reason for the sudden increase in idle speed when releasing the accelerator and pressing the clutch?
3 Answers
The reason for the sudden increase in idle speed when releasing the accelerator and pressing the clutch is: 1. The throttle valve's opening and closing position is inaccurate; 2. The throttle valve's opening and closing mechanism is damaged. The function of the car accelerator is: 1. By controlling the amount of pedal pressure, the engine speed can be controlled; 2. The accelerator controls the carburetor to determine the engine's output power. The working principle of the car accelerator is: When the accelerator pedal is pressed, it directly controls the throttle valve. The throttle valve opening will increase, allowing more air to enter the engine. At this time, the ECU will command the fuel injection system to inject more fuel, causing the engine speed to rise and the car to accelerate.
A few days ago while driving, I encountered the same situation - after releasing the accelerator and pressing the clutch pedal, the idle speed suddenly surged. This is mainly related to the overly sensitive reaction of the engine's electronic control system. When releasing the accelerator, the system assumes the engine is about to stall, so it reduces fuel injection. But the moment the clutch is pressed, it completely disconnects the transmission load, causing the ECU to mistakenly judge that increased fuel injection is needed to maintain idle balance. Over time, carbon deposits accumulate on the throttle body or idle control valve, making sensor signals inaccurate. Regular cleaning of these components can prevent the issue. If neglected, fuel consumption will skyrocket and may even cause starting difficulties. I recommend purchasing some cleaner for maintenance or visiting a professional shop for comprehensive inspection. This problem is more common in older models, like my five-year-old manual transmission car - extra attention is needed for RPM fluctuations after every cold start.
A common customer complaint during car repairs is the sudden surge in RPM when releasing the throttle and pressing the clutch. The root cause often lies in a malfunctioning idle control system. Releasing the throttle is meant to return the engine to idle, but pressing the clutch removes the load, causing the ECU to mistakenly believe additional fuel injection is needed to maintain stability. The most common culprits are carbon buildup in the throttle body or a faulty position sensor, leading to incorrect signal transmission. Aging wiring or loose connectors can also exacerbate the issue. When troubleshooting, start with the basics: disconnect the power, clean the throttle body and mass airflow sensor, and ensure no dirt is affecting performance. If the problem persists, measure sensor resistance or scan for trouble codes using a diagnostic tool. Delaying repairs can lead to wasted fuel or damage to electronic components, so don’t wait until major issues arise. Regular maintenance during daily driving can prevent such problems proactively.
