4 Causes engine high rpm at idle

The car ages and history of uncontrolled vehicle maintenance are the beginning of the cause of high rpm at idle. Usually, the engine rpm will return to idling rpm (800-900 rpm) when the engine temperature has reached its working temperature. It will certainly be different if the problem of high rpm has hit your car.

The characteristic of a car engine that has a high rpm at an idle problem is that the engine rpm will always be above 1000 rpm even though the engine temperature is already hot and has reached its optimal working temperature.

The engine with a high rpm problem can make us difficult to control the vehicle's speed during driving. It is very dangerous if the problem is not immediately repaired.

So, what are the causes of this high rpm at idle? Here are the causes that we know about high rpm at idle that hit your car.

1. Bad water coolant temperature sensor

The cause of high rpm at idle, which is quite often found, is a bad water coolant temperature sensor. The water coolant temperature sensor, also known as the Water Temperature Sensor (WTS) or Coolant Temperature Sensor (CTS), is a sensor used by the ECM to determine the current condition of engine temperature and temperature.

By knowing the engine temperature condition and some data from other related sensors, the ECM will determine the amount of fuel that must be injected into the combustion chamber. For example, when the engine temperature is cold, the ECM will increase the amount of fuel injected into the combustion chamber.

The increase in fuel injections will also be followed by several actuators such as Fast Idle Air Valve (FIAV) and Idle Speed Control (ISC), which will open wider so that the number of incoming air increases according to the amount of fuel injected.

A large amount of fuel and air entering the engine will automatically make the engine rpm increase (increase). So don't be surprised if in the morning, when a new car engine is turned on, we often find the engine rpm will be high for a while (can be more than 1000rpm) and then slowly drop to a normal idling rpm condition.

After the engine temperature is hot and close to the engine working temperature, the ECM will change the amount of fuel injected. The engine speed becomes stable and returns the ISC and FIAV positions to idling rpm conditions.

When the Water Temperature Sensor is damaged, the ECM will not know the actual engine temperature conditions. As a result, the ECM will enter "Fail-Safe" mode and set the engine temperature to a fixed and the same value.

In addition, the ECM will also make the FIAV and ISC remain wide open according to the set value when "Fail-Safe" occurs. As a result, this condition will make the car's rpm high. Even after the engine has reached its normal working temperature, the car's rpm will remain high.

2. Bad Fast Idle Air Valve

The throttle body uses the Fast Idle Air Valve (FIAV) to help the engine warm up when the engine is cold in some vehicles. This Fast Idle Air Valve is generally found in cars whose ISC system uses a DC motor.

This FIAV works based on changes in the coolant temperature of the radiator. Therefore, a throttle body with FIAV must have a bypass hose flowing to and from the radiator.

The function of this FIAV is to open the air duct when the engine temperature is cold. The goal is to increase air when it is cold and accelerate the engine heating process. When the engine temperature is hot, then the wax/pellet on this FIAV will expand and make the valve close and stop the air flowing through the valve.

When the FIAV is damaged, the valve will always be open due to pressure from the valve spring. It will increase the amount of air that enters the engine to make the car's rpm high.

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3. Throttle valve position does not close tightly

Throttle valve position not closing tightly can also be the cause of high rpm at idle. Generally, this happens because the inside of the throttle body connected with the Throttle Valve is worn out so that the throttle valve cannot close tightly.

As a result, air will flow through the gap between the throttle valve and the worn throttle body. This condition will disrupt the work of the ISC as a whole and make a mismatch between the ECM data and the amount of air entering so that it will cause the car's rpm to high.

In addition to wearing and tear, the throttle valve position that does not close tightly and causes high rpm at idle can also be caused by the Fixed Screw Adjusting Screw (Fixed SAS).

In some car brands, there is a Fixed SAS component in the throttle body. This Fixed SAS position has actually been set by the factory and is not recommended to be reset. However, it could be that Fixed SAS has been tampered with so that its position is no longer under the factory settings.

As a result, it can make the car's rpm high because the throttle valve position does not close tightly, and air leaks in from the gap.

4. Bad Idle Speed Control (ISC)

Even though a damaged Idle Speed Control causes more rpm to fluctuate and become unstable, a damaged ISC can also cause high rpm. Even two symptoms can co-occur, namely high car rpm and up and down rpm (rpm swinging above 1000rpm). ).

As already discussed in the characteristics of a damaged ISC, the ISC stabilizes the idling rpm in all engine working conditions. For example, shortly after accelerates. The ISC will maintain the idling rpm so that the engine does not stop. Or, when the engine is under load, the ISC will adjust the idling rpm by raising it slightly higher than the idling rpm, so the engine does not stop.

When the ISC is damaged, especially when it is in the open position, it will automatically increase the amount of air that enters and cause an increase in engine rpm. As a result, the car's rpm will also be high.