RPM Fluctuation While Driving [Causes & How to Fix]

When the RPMs (Revolutions Per Minute) of a car’s engine go up and down, it indicates an issue with its performance. Various factors, such as a problem with the air intake system, fuel system, ignition system, or vacuum system, can cause this.

Other possible causes include worn or damaged spark plugs, a clogged fuel filter, low oil pressure, or a malfunctioning sensor or control module.

RPM fluctuations may also be caused by a problem with the vehicle’s transmission, such as a slipping clutch or torque converter.

Here’s a deep dive into the causes of this issue:

1. Dirty or Faulty Air Filter

A dirty air filter can cause restricted airflow to the engine, which can cause RPM fluctuations. A build-up of dirt and debris can cause a dirty air filter over time or due to a malfunction in the air intake system.

A faulty air filter can also cause similar issues if it cannot filter the air properly.

Fix:

• Locate the air filter in the air intake system; it’s usually located near the front of the engine compartment.
• Remove the air filter by releasing the clips or latches holding it in place or removing any screws or bolts that secure it.
• Inspect the air filter; if it appears dirty or damaged, replace it with a new one.
• If the air filter is clean, it can be reinstalled and secured properly.
• Start the engine and check for any improvements in RPM fluctuations.

2. Vacuum Leaks

Vacuum leaks occur when there is a break in the vacuum hose or a malfunctioning vacuum component, which can cause the engine to run lean.

Running lean means, there’s not enough air and too much fuel in the air-fuel mixture, which can cause RPM fluctuations.

A vacuum leak can also cause a change in engine performance and can affect the fuel economy of the vehicle.

Fix:

• Locate the vacuum hoses and components that may be causing the leak. This could involve using a vacuum gauge, a smoke machine, or a stethoscope to trace the leak.
• Once the leak is located, repair or replace the damaged hose or component.
• Start the engine and check for any improvements in RPM fluctuations.

3. Incorrectly Adjusted Carburetor or Fuel Injection System

The carburetor or fuel injection system is responsible for delivering the correct amount of fuel to the engine.

If these systems are not adjusted properly, they can cause RPM fluctuations. A mechanic or trained professional can adjust the carburetor or fuel injection system.

Fix:

• Locate the carburetor or fuel injection system.
• Use a carburetor or scan tool to adjust the system according to the manufacturer’s specifications properly.
• Start the engine and check for any improvements in RPM fluctuations.

4. Worn or Damaged Spark Plugs

Spark plugs are responsible for providing the spark that ignites the fuel in the engine. Worn or damaged spark plugs can cause misfires which can cause RPM fluctuations.

Worn electrodes, a build-up of carbon or oil on the plugs, or a failure in the ignition system can cause a misfire.

Fix:

• Locate the spark plugs in the engine.
• Remove the old spark plugs using a spark plug socket and a ratchet.
• Inspect the old spark plugs for wear or damage, such as worn electrodes and the build-up of carbon or oil.
• Replace the old spark plugs with new ones specified by the manufacturer for the specific make and model of the vehicle.

5. Malfunctioning Ignition System

The ignition system is responsible for providing the spark that ignites the fuel in the engine. If the ignition system is not functioning properly, it can cause RPM fluctuations.

A faulty ignition coil, a bad spark plug, or a faulty ignition control module can cause a malfunctioning ignition system.

Fix:

• Locate the ignition system components, such as the ignition coil, spark plug, and ignition control module.
• Use a diagnostic tool to check for any codes or issues with the ignition system.
• Replace any faulty ignition components and repair any wiring issues.

6. Clogged Fuel Filter

A clogged fuel filter can restrict fuel flow to the engine, causing RPM fluctuations. A clogged fuel filter can be caused by a build-up of dirt, rust, and debris or by a problem with the fuel pump or fuel injectors.

Fix:

• Locate the fuel filter. It’s usually located near the fuel tank or fuel pump.
• Remove the old fuel filter by releasing the clips or latches holding it in place or removing any screws or bolts that secure it.
• Inspect the old fuel filter for any restrictions, such as dirt, rust, and debris.
• Replace the old fuel filter with a new one.

7. Low Oil Pressure

Low oil pressure can cause the engine to run poorly, resulting in RPM fluctuations. Also, a low oil level, a worn oil pump, or a clogged oil filter can cause low oil pressure.

Fix:

• Locate the oil filter and oil pressure sensor.
• Check the oil level and condition.
• If necessary, replace the oil and filter.

8. Worn or Damaged Belts or Pulleys

Belts and pulleys transfer power from the engine to various components. Worn or damaged belts and pulleys can cause RPM fluctuations by causing slippage or misalignment of these components.

Worn or damaged belts and pulleys can be caused by improper installation, age, or exposure to heat and chemicals.

Fix:

• Locate the belts and pulleys that may be worn or damaged.
• Remove the old belts and pulleys by releasing the clips or latches holding them in place or removing any screws or bolts that secure them.
• Inspect the old belts and pulleys for wear or damage, such as fraying, cracking, or misalignment.
• Replace the old belts and pulleys with new ones.
• Check the tension and alignment of the belts and pulleys to ensure proper operation.

9. Leaking or Stuck Open Throttle Body

The throttle body controls the air entering the engine. If the throttle body leaks or gets stuck open, it can cause RPM fluctuations.

A leaking or stuck open throttle body can be caused by a build-up of dirt and debris or by a malfunctioning throttle position sensor.

Fix:

• Locate the throttle body.
• Clean or replace the throttle body
• To clean the throttle body, remove it from the vehicle and use a throttle body cleaner and a brush to remove any dirt and debris.
• To replace the throttle body, remove it from the vehicle and install a new one, making sure to align and secure it properly.

10. Failed Sensors or Control Modules

The engine relies on various sensors and control modules to operate properly. If any of these components fail, it can cause RPM fluctuations.

Various issues, including age, exposure to heat and chemicals, or electrical system problems, can cause failed sensors or control modules.

Fix:

• Locate the sensors and control modules that may be failed.
• Use a diagnostic tool to check for any codes or issues with the sensors and control modules.
• Replace any failed sensors or control modules with new ones.

Note: All these causes listed are just a few of the many reasons why your may be experiencing RPM fluctuations.

However, if these causes don’t pertain to you, you should take your car to a professional mechanic for proper diagnosis and repair.

Nonetheless, we will still discuss some processes you can use to troubleshoot the exact issue with your car’s RPM fluctuation. Keep on reading!

How to Troubleshoot RPM Fluctuations While Driving

Here are some steps to troubleshoot RPM fluctuations:

• Check the diagnostic codes
• Check the Throttle Position Sensor (TPS)
• Check the mass air flow sensor: If the diagnostic codes indicate the MAF is the problem, replace it with a new one.
• Check the ignition system.
• Inspect the fuel system
• Check the vacuum system
• Check the timing belt and pulleys
• Check the Engine sensors
• If the diagnostic codes do not provide any information about the cause of the RPM fluctuations, have a professional mechanic inspect the car for other possible causes.

How Can RPM Fluctuation Be Prevented?

1. Regular Scheduled Maintenance

A regular maintenance schedule is essential in preventing RPM fluctuations. This includes regular oil changes, air filter replacements, fuel filter replacements, spark plug replacements, and belt and pulley inspections.

Following the manufacturer’s recommended maintenance schedule can help ensure your vehicle runs at its best and prevent issues that could lead to RPM fluctuations.

2. Regular Inspection of the Vehicle’s Engine and Transmission

Regularly inspecting the engine and transmission can help identify any issues that could lead to RPM fluctuations.

This includes checking for vacuum leaks, inspecting the carburetor or fuel injection system, and checking the ignition system.

Having a professional mechanic inspect the vehicle can also help identify any potential issues and prevent RPM fluctuations.

3. Prompt Repairs of Any Issues Identified

Any issues identified during regular maintenance or inspections should be addressed as soon as possible.

Prompt repairs can help prevent RPM fluctuations and ensure the vehicle runs smoothly.

4. Use the Correct Type and Grade of Oil

Using the correct type and grade of oil can help prevent RPM fluctuations. The recommended oil type and grade can be found in the vehicle’s owner’s manual. Using the wrong oil can damage the engine and cause RPM fluctuations.

5. Use the Correct Type of Fuel

Using the correct type of fuel can help prevent RPM fluctuations. The recommended type of fuel can be found in the vehicle’s owner’s manual.

Using the wrong type of fuel can cause damage to the engine and lead to RPM fluctuations.

6. Avoid Overloading the Vehicle

Overloading the vehicle can cause stress on the engine and transmission and lead to RPM fluctuations. It is important not to carry more weight than the vehicle is rated for and not tow more than it is rated for.

7. Properly Inflate the Tires

Properly inflating the tires can help prevent RPM fluctuations. This includes checking the tire pressure regularly and inflating the tires to the recommended pressure.

Underinflated tires can cause stress on the engine and transmission, leading to RPM fluctuations.

8. Avoid Aggressive Driving

Aggressive driving can cause stress on the engine and transmission, leading to RPM fluctuations. It is advisable to avoid over-revving the engine and not shifting gears too quickly.

In addition, avoiding hard braking, accelerating, and maintaining a steady speed can help prevent RPM fluctuations.

Conclusion

RPM fluctuation while driving is caused by various factors, such as issues with the air intake system, fuel system, ignition system, or vacuum system leak.

Other possible causes include worn or damaged spark plugs, a clogged fuel filter, low oil pressure, or a malfunctioning sensor or control module.

It is important to take preventive steps such as regularly scheduled maintenance, regular inspection of the vehicle’s engine and transmission, prompt repairs of any issues that are identified, using the correct type and grade of oil, using the correct type of fuel, avoiding overloading the vehicle, properly inflating the tires and avoiding aggressive driving.