Why does the car rev without pressing the accelerator when starting?

[ChaseAnn]

The reason why the car revs without pressing the accelerator when starting is due to a problem with the idle speed motor. It is necessary to check the idle speed motor and clean the throttle body. The car accelerator is a device on the internal combustion engine that regulates the fuel supply. During driving, the driver adjusts the amount of pedal press to control the engine's air intake, thereby regulating the engine speed. The steps for starting a car are: 1. Press the start button, and after the ACC light comes on, press it again for the vehicle to perform a self-check; 2. Press the brake, then press the one-button start to ignite and start the engine; 3. Release the foot brake and let the car warm up in place; 4. Press the foot brake, shift to D gear, and release the handbrake; 5. Slowly release the foot brake, add some throttle, and the start is complete.

[McElizabeth]

Last time I encountered this issue, I found the throttle body was too dirty. When starting the car, the ECU increases idle speed for quick warm-up. But if carbon buildup in the throttle body is severe, the throttle plate may stick in a more open position, allowing excess air to enter and causing engine revving. Another possibility is the idle control valve being stuck by sludge and unable to return to position, or the coolant temperature sensor falsely reporting low temperature signals causing the ECU to continuously enrich the mixture. My old car improved immediately after cleaning the throttle body, and I also checked the vacuum lines for leaks. This problem is particularly noticeable in winter, and short-distance driving makes carbon buildup more likely. I recommend checking it every 20,000 kilometers or so.

[VonNoah]

A common scenario during car repairs involves checking four key areas: First, check if the throttle position sensor signal is drifting. Second, verify if the air flow meter readings are distorted. Third, inspect the fuel pressure regulator diaphragm for damage causing abnormal fuel return. Fourth, check if the carbon canister solenoid valve is stuck open, leaking fuel vapor. Turbocharged cars are particularly sensitive to these issues. For instance, a recent customer had unstable intake pressure due to a stuck bypass valve. A quick diagnostic method is to unplug the air flow meter connector and observe RPM changes, but it's best to connect an OBD scanner to read real-time data streams to avoid unnecessary part replacements and wasted money.

[Collin]

High revving during cold starts is actually normal, as the ECU actively increases idle speed to warm up the engine. However, if it continues when the engine is hot, there's likely an issue. From my experience: during a morning start, the RPM should drop from around 1500 to 800 within 30 seconds for proper operation. If high RPM persists, first check if the air filter is too dirty, affecting air intake calculations, then inspect whether the spark plug gap is too large, causing ignition delay. Occasional high revving might be due to sudden temperature changes causing ECU adaptation deviations, which usually resolve after driving a few kilometers. But if it occurs weekly, it should be taken seriously—don't wait until fuel consumption spikes before addressing it.

[DelEmersyn]

Electronic throttle vehicles are prone to this issue. Abnormal signals from the throttle pedal position sensor can cause the ECU to misjudge the driver's intention, or slipping of the motor drive gear can lead to uncontrolled throttle opening. When I previously performed matching on my brother's car, I found that incorrect brake switch signals could also cause engine revving, as the ECU interpreted it as a hill start condition. For new cars, it might be a software bug, and updating to the latest program at the 4S shop often resolves it. Key checks include inspecting whether the wiring connectors are oxidized and ensuring there are no loose ground connections.

[LillianaAnn]

Engine surging is essentially caused by an imbalance in the air-fuel mixture. Fuel injector leakage can lead to an overly rich mixture during cold starts, forcing the ECU to compensate by increasing air intake. A leaking intake manifold gasket creates a vacuum leak, resulting in an overly lean mixture, prompting the ECU to increase fuel injection. Additionally, a clogged crankcase ventilation valve (PCV) can cause oil vapor to backflow, interfering with the oxygen sensor signal. During my own troubleshooting, I found that pinching the PCV valve hose during surging—if the RPM drops—indicates it's the culprit. It's advisable to check if smoke emerges from the oil filler cap. Replacing the PCV valve costs just a few dozen dollars.