What Causes a Car to Rev Without Pressing the Accelerator?

[ChristopherLee]

When a car revs without pressing the accelerator, it is mostly due to a faulty idle speed motor. Checking the idle speed motor and cleaning the throttle body should resolve the issue. Below is a detailed introduction to the car accelerator: 1. The car accelerator is a device on an internal combustion engine that controls the fuel supply. 2. While driving, the driver controls the amount of air intake by adjusting the pedal pressure, thereby regulating the engine speed. Here are the correct steps to press the accelerator: 1. Place your right foot on the center of the accelerator pedal, pressing with the ball of your foot near the toe. 2. Press the pedal gently and release it slowly; avoid sudden or excessive force, and maintain a smooth motion. 3. When not accelerating, do not keep your foot on the accelerator pedal; it is best to place it on the brake pedal to ensure timely braking in case of emergencies. 4. Occasionally revving the engine can help remove minor carbon deposits. You can rev the engine before shutting it off to expel carbon deposits, though this method is ineffective for old or heavy carbon buildup.

[LaCecilia]

My car has experienced this issue before, and the sudden RPM surge at idle is really scary. The most common cause is excessive carbon buildup in the throttle body causing it to stick, which makes the ECU compensate by adding fuel when it doesn't receive the correct signal. It could also be a faulty idle air control valve, as this component specifically regulates the air intake at low RPMs. A malfunctioning throttle position sensor can also cause misjudgment, leading to incorrect fuel injection by the engine. Additionally, some older cars with mechanical throttle cables might have sticking issues that require lubrication checks. Since this problem involves multiple systems, I recommend starting with a throttle body cleaning. If that doesn't work, then check the sensor circuits.

[MacIvan]

After driving for over a decade, I've found that revving the engine in neutral is mostly caused by electronic system malfunctions. The throttle position sensor is the most common culprit—when it sends incorrect opening data to the ECU, the computer ends up mismanaging fuel injection. A sticking idle control valve can also cause this, especially noticeable during cold starts. Air leaks in the intake system, like cracked vacuum hoses, disrupt the air-fuel ratio, prompting the ECU to compensate with extra fuel. A faulty fuel pressure regulator similarly leads to excessive fuel injection. Don't delay fixing this—it'll just waste more gas and risk damaging the catalytic converter. Get the trouble codes read immediately.

[SanBella]

I have a deep personal experience with this issue. Last time after maintenance, the technician forgot to install the air filter box, resulting in air leakage that caused the engine to automatically compensate with extra fuel. In fact, the main cause is the air-fuel ratio imbalance, including: inaccurate mass air flow sensor readings, oxygen sensor poisoning, or a stuck charcoal canister purge valve—all of which can cause the ECU to misjudge the mixture concentration. On the mechanical side, it could be a vacuum hose leak or a faulty PCV valve. I recommend first checking if the air filter is properly installed, then using a cleaning spray to listen for leaks along the hoses, and finally connecting a diagnostic scanner to monitor real-time data streams.