RPM Fluctuation while Driving [Causes & How to Fix]

RPM Fluctuation can affect your driving experience, which may even lead to damage.

Whether you’re a seasoned car owner or a new driver, understanding RPM fluctuation and how to handle it is essential to keeping your car running smoothly and safely on the road. 

Are you experiencing RPM fluctuation while driving and unsure what’s causing it? 

Make sure you read this blog post till the end, as we will explore the common causes of RPM fluctuation and how to fix it. However, before we start, let’s first understand RPM and its role in automobiles. 

RPM Fluctuation while Driving

What is RPM?

RPM is a measurement that shows the number of times each piston in your car’s engine rises and falls and the number of rotations the crankshaft completes in a minute. It’s an acronym for “Revolution Per Minute”. 

It is located on your dashboard and monitored by your automobile on the tachometer–this device measures the angular speed of a rotating shaft in revolutions per minute (RPM). Depending on how quickly you’re driving, you’ll typically see an increase or decrease in RPM.

Causes of Car RPM Fluctuation While Driving

1. Worn Out Plugs

Worn-out plugs are one of the common causes of RPM fluctuation. They are responsible for igniting the fuel in the piston at the right time. 

When these plugs wear out, they won’t be able to fulfill their purpose effectively, so they ought to be replaced as soon as possible.

2. Faulty Transmission

Defective transmission is another common reason RPM will fluctuate while driving. For automatic vehicles, the RPM revolves when the gear’s clutch or friction disc of that particular gear is slipping. It can also happen when downshifting to a lower gear or when the shift modulator is faulty.

With a manual transmission, a worn clutch can slip at every point you press the accelerator under load, which can cause your car’s RPM to fluctuate.

3. Damaged Crankshaft Position Sensor 

A crankshaft position sensor is a tool that helps you keep track of your crankshaft’s location or its rate of movement. The engine control module then uses this data to regulate the timing of the ignition system and fuel injection.

Therefore, the crankshaft position sensor malfunctions if the engine does not receive accurate information regarding the position of the crankshaft, and it may cause the RPM to fluctuate.

4. Vacuum Leakage

You might have a vacuum leak if your RPM is constantly changing when you’re driving, especially while you’re speeding.

Vacuum leakage usually occurs in your engine bay. And it causes fluctuating RPM and erratic idling, decreased fuel efficiency, the check engine light, and a hissing sound. And it disrupts the fuel-air mixture in the engine, resulting in a lean fuel-air combination.

5. Broken Throttle Pedal Position Sensor

If your TPS is malfunctioning, it can cause your car to accelerate on its own. Which could result in rough idle and observable RPM fluctuations.

Rust or dirt on the contacts of a throttle pedal position sensor will typically result in malfunction, which might require a replacement.

6. Fuel Injector Blockages

Delivering the gasoline required for the engine to function effectively is the function of the fuel injector. The engine may need more gas if the injectors become clogged (by dirt and debris).

Dirt in the fuel injector can lead to many problems. This includes jerky motions, variable RPM, or the automobile needing to accelerate as it should. You can clean the fuel injectors or replace them due to wear and tear.

7. Clogged Air Filter

The air filter needs to capture the dirt to keep the air clean before it enters the engine, which can also cause it to get clogged.

And if the airflow in the engine is insufficient due to a dirty air filter, it can result in RPM variation and acceleration delays. If you discover this is why RPM fluctuates in your car, you would need to change it to get it fixed.

8. Faulty Tachometer 

A tachometer is a device that monitors your RPM. When it is broken, it can cause the RPM to fluctuate and you might need to replace the entire group of instruments of the tachometer.

Although rare, you should not disregard the possibility of damage to the tachometer. Therefore, use an OBD2 scanner to detect if your tachometer is faulty.

How to Fix a Fluctuating RPM

Fixing RPM fluctuation is a DIY skill if you are familiar with automobiles–it is effortless to attempt. You can check your spark plugs to see if they need to be changed, clean the fuel injectors, and replace the air filter.

Considering the age of your car, it is also a good time to change your gearbox fluid if you still need to do that. However, if you cannot diagnose any problem, you will need to contact a professional to help you fix it.


What is an Automatic Transmission’s RPM Range?

 The RPM range for shifting gears is between 1200 and 1800. However, this range varies from car to car and it is also affected by your gearbox type.

Why Does the RPM of my Automobile Fluctuate at a Steady Speed?

The engine downshifting and upshifting while the automatic transmission is in use may cause RPM to fluctuate steadily.

This could result in a slight acceleration of your vehicle, which frequently happens due to a heavier load. But it might indicate transmission problems.

Read: How to Remove Freon from Car without Recovery Machine


You can see that various factors, such as worn-out spark plugs, clogged air filters, and vacuum leakage, can cause RPM fluctuation.

Therefore, paying attention to your car’s RPM and fixing any issue as soon as possible is essential to avoid potential damage or safety hazards. 

Remember, your car’s RPM gauge is an important indicator of your car’s overall health. Regular maintenance and proper diagnosis by a qualified mechanic can help prevent and solve issues related to RPM fluctuation.