3 Main Causes of Car RPM Up and Down + Solutions

Mech4cars.com – 3 Main Causes of Car RPM Up and Down + Solutions – Unstable engine RPM, could indicate a problem with the engine’s air induction system. The risk, of course, we will find it difficult to control the speed of the car at low speeds and the shift of the transmission lever also becomes less soft. And even in some cars, this incident can cause the car engine to die.

Read more: Causes of Rpm Up and Down when AC is On

So what happened? how to handle it? see the causes and how to overcome the car RPM up and down below.


Table of Contents

3 Main Causes of Car RPM Up and Down + Solutions

Air and fuel that enter the combustion chamber greatly affect the engine RPM. Logically, when a little air and fuel enter the combustion chamber, the piston only compresses a little “gas” in the compression stroke. This results in even small combustion results and the engine RPM can be slow.

Car RPM Up and Down

In addition, the gas valve also affects the RPM. The gas valve works by closing the air duct to the engine. If this channel is closed, the piston movement during the suction stroke will be restrained. This will certainly slow down the engine RPM.

But these three things are very sensitive, just a little different the engine RPM can change. Therefore, if these three things are not stable when the engine is running, then the RPM will automatically go awry. Even cars with EFI technology, also often get this problem.

Read more: Reasons for Rough Idle When Engine is Hot

Why do we often encounter this problem?

This is because, in the injection system, the ECU regulates the fuel supply in a closed manner. So how do we fix this if we don’t know the scheme? Especially in the latest type, the engine already has drive-by-wire technology, namely gas wireless valve technology (an electric motor regulates valve opening).

Sometimes the gas valve often goes wrong and the result can open and close itself even though we don’t touch the gas pedal. So what’s the solution? Calm down, in the following article we will discuss thoroughly the causes of car RPM going up and down and how to overcome them.

There are many things that cause the RPM on a car to be unstable, including the following.

1. Idle speed control

Idle speed control becomes an actuator in the EFI system whose function is to adjust the idle RPM. The way it works is by using a solenoid valve to open and close the carburetor’s idle channel.

Car RPM Up and Down
Edited picture from: shopee

However, if the ISC is dirty and we rarely clean it, then the air supply from outside to the intake manifold will obviously be hampered. As a result, there is a delay that makes the air supply to the engine unstable as long as the engine is idle. So the RPM can go up and down.

Read more: 7 Causes of Engine RPM Problems Too High During Acceleration And How To Overcome It

To overcome this, you need to diligently clean the ISC actuator and idle channel holes. The method is quite easy, you just need to open the ISC and clean the valve. Also, clean the idle hole using a spray-type carburetor cleaner.

2. Mass Air Flow

Mass airflow is located in the air filter tube. Its function is to detect how much air mass enters the engine based on its flow speed.

Because it is located in the air filter area, this sensor is also prone to getting dirty. So that the inaccurate readings on the MAF sensor cause the data sent by the sensor to be inconsistent. As a result, because the ECU also uses this data to determine the quantity of gasoline, the volume of gasoline that comes out of the injector is also not constant. So the RPM can go up and down.

Car RPM Up and Down

Usually, the symptom of an inaccurate MAF sensor also causes the check engine light to turn on.

Read more: 7 Symptoms of Mass Air Flow Sensor Damage

To fix this, we need to first detect whether the problem lies with the sensor or in the sensor circuit. Check the cables and cable connectors that are connected to the MAF sensor first. Next, try to clean the MAF sensor section using a carb cleaner or carbon cleaner and the like.

Make sure when doing this check, you have unplugged one of the cables on the battery. The reason is that if we unplug the engine while the electricity is still connected, it is feared that it will cause new problems.

When finished, try to start the machine. If the RPM is still unstable then there are two possibilities.

There are other causes that make the engine RPM go up and down (3rd cause) The MAF sensor is damaged, to prove it requires a scan tool.

3. Dirty throttle body

Engines that use the TAC or drive-by-wire system, no longer use a cable wire to connect the gas pedal to the throttle body. An electric motor is located inside the gas valve which automatically opens and closes at the command of the APP sensor on the gas pedal. But cars like this are the ones that experience RPM up and down the most.

Car RPM Up and Down

The reason is that cars with TAC technology are more sensitive to changing conditions. Because it does not reflect on just one sensor, but there are many sensors that support TAC performance.

Read more: How to Clean the Throttle Body Yaris And New Limo?

When there is dirt at the base of the valve leaf, the idle RPM can go up and down. To prove it, remove the throttle body from the car engine, then pay attention to the valve leaf area, there will be black dirt on the valve wall. Dirt is what causes the engine RPM is not crazy.

The solution, we must immediately clean the throttle body when these symptoms appear. If not cleaned immediately, then the problem will trigger problems with other components. Because that’s the risk of EFI cars. Each component is interdependent.

You can do this cleaning yourself or it can be done at an authorized repair shop. The trick, as usual, remove the battery and disconnect the TAC electrical connector. Remove the throttle body component and clean it using a carb cleaner or the like.

Unstable Engine RPM Is Normal When?

In some conditions, the engine rpm that sometimes goes up and sometimes goes down without gas is also a normal thing, even if it doesn’t happen, it could indicate a malfunction. This condition occurs when;

1. AC compressor and fan working

When the magnetic clutch on the compressor is connected, the engine load will increase because it will move the AC compressor which pumps freon. In addition, the electrical load of the machine also increases because the extra fan automatically turns on.

Read more: Causes of AC Not Cold when the Car is Stopped

If the engine RPM remains stable while these two components are working, the engine could potentially die. For that, the ECU automatically increases the engine idle RPM.

2. When the battery voltage is low

The normal battery voltage is 12 Volts, when the engine is running normally reaches 14 Volts. If the car’s electrical load is large enough, the system requires a large power value. So it forces the battery to work more extra.

If we let this happen, the battery will run out. So we have to increase the engine RPM with the aim of the alternator working extra to supply electricity to the battery.

Read more: Causes of Easy Car Battery Heat in Your Car

How to fix the above problem only if you are really familiar with EFI systems. If you are still not familiar with it, it would be nice to take your car to an official repair shop. In the workshop, the health of the car will be guaranteed because there are certified mechanics and complete tools.

Tips you can do to prevent RPM from going up and down;

  • Always clean the air filter regularly at least once a month because the three causes above were originally from a dirty air filter.
  • Always use high-octane gasoline
  • Don’t ignore your vehicle service schedule, especially if your car already has a drive-by-wire system. Periodic service becomes quite important

Thus our short article about the causes of unstable car RPM. Hopefully, our automotive knowledge will increase, and hopefully, it will be useful.

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