Car Revving On Its Own When Stationary – What is the reason?

One of the most common problems for car drivers is the car revving on its own when stationary. This failure not only causes inconvenience during operation but also threatens your safety.

So what is its cause? Let’s learn more about this topic through the following article.

Are Self-Revving Cars Safe?

Car Revving On Its Own When Stationary

Imagine you are driving every day when the car jumps up suddenly like someone is trying to press the gas pedal.

Sometimes, this could be because the driver misplaced his foot between the brake pedal and the gas pedals.

However, if the car suddenly loses speed control without any driver intervention, it experiences a serious revving problem.

Engine revving up is embarrassing for drivers on the road and can lead to many tragic accidents.

According to statistics, many manufacturers have to recall a series of cars yearly to check and fix this technical error.

Why Car Revving On Its Own When Stationary?

The cause of the car revving on its own while driving may be due to the wear and tear of the equipment during prolonged use, technical errors right from the manufacturing stage (Toyota’s accelerator scan in 2010), or a few other reasons like:

Idle Speed Control Valve Problem

Idle Speed Control Valve Problem

The degradation of the idle speed control system is one of the main reasons why your car revs up on its own.

For vehicles with fuel injection engines, the driver does not need to press the pedal when starting, which means the throttle plate does not open.

For the engine to get air, we need the idle control valve to control the wind to bypass the closed throttle.

This helps control the idle speed to match the engine conditions. However, the idle issues (due to oil or dirt) will cause the vehicle to operate poorly, stall, cause sudden acceleration, etc.

You can fix a stuck valve simply by cleaning, but if the valve is damaged due to motor failure, it needs to be replaced with a suitable type.

Degraded Air Filter

Degraded Air Filter

The engine air filter is located in the car engine compartment, just below the bonnet.

It acts as a “lung” to help clean the air and prevent dirt and impurities before entering the combustion chamber so as not to affect the vehicle’s operation.

After the operation, impurities and dirt will stick to the air filter. If not cleaned or replaced periodically, they will fill up the air vents, preventing air from entering the combustion chamber.

From there, they will seriously affect the combustion process, reduce engine performance, reduce the durability of engine parts, cause engine heat, and produce soot in the combustion chamber, causing the car to rev itself when idle.

MAF Sensor Problem

MAF Sensor Problem

A car engine revving itself could be a warning sign that there is a mechanical issue with the mass air flow sensor.

The MAF is the part located between the filter and the intake manifold.

Its function is to determine the speed and adjust the amount of air entering the fuel injection system of the internal combustion engine accordingly.

In an internal combustion engine, standard air mass balances the central control unit and provides accurate information to the combustion chamber.

Malfunctioning MAF will affect engine stability, reduce power, stall, faulty ignition, etc.

At this time, car owners can find out the signs of a faulty intake air flow sensor at home or take the vehicle to a reputable service center for proper handling.

Dirt On The Cars Throttle Body

Dirt On The Cars Throttle Body

When you see your car revving on its own when started, try to check the throttle body because it is most likely something wrong.

The throttle is a place to store air when entering the engine, and it only opens when the driver steps on the accelerator. The opening will depend on how hard the accelerator pedal is pressed.

After long use, the throttle valve can become clogged with dirt and reduce engine performance.

You notice black soot clinging to the inside and outside of the intake manifold. This long-term situation will cause many negative effects on your car.

Specifically, the dense layer of dirt on the throttle body loses the standard head position of this part. This reduces engine performance and leads to difficulty starting or revving.

The more dirt and dust attached, the more it will cause the throttle plate opening to be wrong; as a result, it will push the fuel to spray inappropriately.

This is very dangerous when the driver is on the road because it can cause the car to turn off suddenly.

Although this error costs you more fuel bills than usual, you can fix it by cleaning issues.

Throttle Position Sensor Error

This part of the throttle body is considered the “soul” of the fuel system.

It ensures the correct amount of air flows from the intake manifold into the combustion chamber by monitoring and collecting data on the position and rotational speed of the engine.

Although the throttle valve has a simple structure, it is still a part that is prone to malfunction after long-term use or lack of regular maintenance.

Once unable to operate at 100% capacity, it can lead to many inconveniences such as stalling, revs on their own, etc.

Some signs of damage include:

  • Vehicles need more fuel than before: When the TPS sensor degrades, the air-to-fuel ratio will no longer meet the standard. Thus, the engine needs more power for normal combustion.
  • Check engine light is on: When the TPS fails, it sends a signal to the central controller.

ECT Sensor Problem

ECT Sensor Problem

An engine coolant temperature (ECT) sensor is used to measure the temperature of the coolant mixture and transmit information to the Engine Control Unit (ECU).

It needs the results to adjust the fuel injection and ignition time and help stabilize the engine temperature.

Currently, some models often mount an ECT sensor on the engine body and add an extra sensor at the outlet of the thermostat valve or on the radiator. This helps to monitor the valve’s working process more accurately.

But like many other parts, ECTS may have some damage after prolonged use, such as The ECU will turn on the check engine light when it receives an error signal that the sensor unit reports.

ECT errors affect the accuracy of the measurement results, which causes the ECU to miscalculate the time and fuel quantity.

For example, when the engine temperature is low, it will inject more fuel to warm up the engine, thereby causing poor fuel economy.

The signal from the faulty sensor causes the cooling fan to operate incorrectly, leading to the cooling water not being cooled, causing the engine to overheat.

Besides, you can also see black smoke coming from the engine.

Coolant Level

The Car's Coolant Level

Today, car owners are familiar with using engine coolant (green or red solution) for their cars.

It has an antifreeze effect when the outdoor temperature is low to protect the water tank from breaking; it helps cool the engine faster than normal water.

Too much heat without cooling in time will reduce the strength of the components and cause them to emit more heat.

The friction force on the engine surface will increase, affecting the vehicle’s performance.

In addition to cooling the coolant, it protects the engine from damage or wear after long use. This solution is the secret to keeping the car in good working order and increasing its lifespan.

According to the professional mechanic, the coolant level is something that needs to be regularly checked because if it is too low, the engine will have to work in a state of overheating, which can cause severe damage.

Faulty Fuel Pressure Regulator

Faulty Fuel Pressure Regulator

Fuel pressure regulator malfunction can also cause a car revs on its own in neutral. This metal device has a cylindrical shape and connects the fuel supply hose to the injector (split tube).

It is responsible for maintaining the fuel pressure at a standard level for the smoothest engine operation, preventing the pipeline from bursting when the fluid rushes back suddenly.

The pressure regulator valve also performs the task of adjusting the input pressure of compressed air in the pipeline, helping to ensure that the fuel entering the combustion chamber will be porous and easy to evaporate to save time.

Damaged pressure regulators will cause insufficient fuel pressure in the injectors, and the air-fuel mixture is not guaranteed.

In addition, it also leads to a lot of fuel consumption due to the pressure difference. The signs you may experience are:

  • Vacuum leaks
  • Strange noise
  • Reduce engine power
  • Black smoke coming out of the exhaust pipe
  • Large amount of exhaust gasses
  • Sudden change in crankshaft speed
  • The accelerator pedal is degraded, even unresponsive
  • Faulty ignition

Therefore, vehicle owners should check this part regularly to detect problems early and promptly handle them.

Cam Phaser Problem

Cam Phaser Problem

The camshaft is a mechanical part of the gas distribution in an internal combustion engine, which transfers energy from one element to another.

This important part helps to operate the valve, contributing to optimal engine performance.

The camshaft operates with the help of the crankshaft at approximately half the speed of the crankshaft.

Depending on the vehicle, the position sensor of this part is different; it may be located on the trigger cover, the side, or the top of the cylinder.

It is not natural that car manufacturers focus on designing and manufacturing camshafts.

It makes the car less prone to problems, provided that the camshaft is located at the top of the engine cylinders.

A damaged camshaft sensor will seriously affect operating performance, causing the car to increase or decrease the throttle.

Faulty Spark Plugs

Are Ignition Coils And Spark Plugs The Same

Spark plug failure is a commonly-known cause of car problems, and car revving failure is no exception.

The spark plug is a part of the ignition system, which plays an important role in the car engine’s operation: generating an electric spark between the center electrode and the grounding side to ignite the fuel in the cylinder.

Its spark-generating process is a reaction between oxygen gas, fuel, and temperature. Bad spark plugs greatly affect the engine performance.

To be more sure, you should check it for signs like:

  • Abnormal fuel consumption 
  • Difficult/no starting 
  • Faulty ignition
  • Strange noise 
  • Unstable engine light
  • Poor performance 
  • Slow response; there is a jerk when operating.

EGR Valve Error 

EGR Valve Error

With the task of bringing part of the exhaust gas back to mix with the intake air, the EGR valve on cars is like a “green lung” to help control and minimize harmful NOx emissions into the environment.

Its arrival has helped manufacturers meet increasingly stringent emissions standards.

However, because the EGR valve is constantly in contact with the exhaust gas in the engine, it is easy to get stuck or clogged due to soot or carbon deposits.

Dirty Fuel Injectors

Dirty Fuel Injectors

The fuel injection system has the advantage of significantly reducing emissions to the environment.

By optimizing the amount of fuel injected, FI helps the engine work stably, increases power and saves fuel.

However, this system also has limitations that users need to understand to use the vehicle properly. Most malfunctions are caused by sensors and actuators with manifestations such as:

  • Car stalls suddenly
  • The car is weak; it is difficult to change the engine speed
  • Hard/impossible to start
  • Revving
  • Vacuum Leaks
  • Large amount of exhaust gasses
  • The warning light is on


Above are the reasons why a car revving on its own when stationary.

To ensure safety during each journey, do not forget to bring the car to the automotive service center for the professional mechanic to check. The early detection of signs will help save time and repair costs.

Hope this article is useful to you. Thanks for reading.

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