6 Common Causes of RPM Fluctuation While Driving

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rpm fluctuation while driving

If you’re a vehicle owner, chances are that at some point in time you have noticed RPM fluctuation while driving. For most drivers, this is a minor annoyance and something they can live with. However, if the RPMs fluctuate enough to make your car feel like it’s shaking back and forth when you step on the gas pedal, then this may be something worth addressing sooner rather than later because there could be an underlying problem. 

If you’re noticing your RPM fluctuating while driving, it is likely due to one of the following six common causes. These are the most common, but not exclusive factors for RPM fluctuation.

What Is RPM?

Before we dive into what causes RPM fluctuation, we should first understand what RPM is.  RPM stands for “Rotation Per Minute.” As a vehicle accelerates or decelerates, it rotates the tires at a certain speed. If you look at your car’s tachometer, you’ll see RPM as a number on the dial.

The tachometer displays your vehicle’s speed in terms of revolutions per minute (RPM). Under acceleration, RPMs will increase as you press the gas pedal. Similarly, RPMs will decrease as you press the brake or let up on the accelerator. Most engines rev up to around 4,000 to 6,000 RPM, though this can vary significantly depending on what kind of car you drive and how powerful it is.

Common causes of car RPM fluctuation

engine cylinder block

There are a couple of things to consider when trying to diagnose a fluctuation in your car’s RPM. If your RPM goes up and down while accelerating it’s likely due to worn-out spark plugs, however, here are some other common causes:

Bad Idle Air Control Valve

When your RPM fluctuates while accelerating, it’s generally due to a problem with the idle air control valve, or IAC, in your automobile. The idle air control (IAC) valve is found on the throttle body of fuel-injected engines, where it communicates with the vehicle’s ECU to electronically regulate airflow to control the engine idle speed.

Oftentimes, when there is a problem with the idle control valve and you’re noticing RPM fluctuation, it’s usually from communication issues. The IAC and ECU need to communicate to properly regulate airflow and maintain steady RPMs. If there is any interference, the IAC cannot work properly and you will likely notice RPM fluctuations. Some other common symptoms of a defective IAC include engine stalling and rough idling.

Vacuum Leaks

If your car’s RPMs fluctuate while accelerating, then you may be dealing with an engine vacuum leak in the engine. A vacuum leak is when there is an interruption in the air flow in the intake manifold or exhaust system of your vehicle. Other signs of a vacuum leak include lower fuel efficiency, a hissing sound, check engine light turning on, power loss, car stalling, and a rough idle.

Take your automobile to a professional mechanic to have the vacuum leak fixed. If you don’t get this fixed right away, it might cause you a lot of trouble. It may also be dangerous to drive and cause an accident if left unchecked.

Worn-Out Spark Plugs

RPM fluctuation is a common symptom of worn-out spark plugs, especially in older vehicles. Spark plugs that are worn out are unable to correctly fire the fuel within the piston at the appropriate time. This might result in sluggish acceleration. When accelerating, your automobile may experience misfires and jerking. Also, if spark plug wires or ignition coils have gone bad you may experience similar symptoms – so keep that in mind.

Poor fuel economy, engine misfires, and significant vibration are other symptoms of worn-out spark plugs. If you notice any of these signs other than fluctuating RPM, you should get your spark plugs changed ASAP.

Faulty Throttle Pedal Position Sensor

When your TPS is broken, it can cause your automobile to accelerate on its own regardless if you’re pressing down on the gas pedal. This can result in a fluctuation of your engine’s RPM. So if you notice your RPM fluctuating while accelerating, it might be due to a faulty throttle pedal position sensor. Other symptoms of a bad TPS include trouble starting up or your engine misfiring.

Dirty Fuel Injectors

Fuel injectors become coated with grime and other substances in the fuel. When this happens, acceleration may become jittery, and attempting to accelerate from a stop or maintain a constant speed can cause the automobile to lose power. Your vehicle’s performance may suffer, and its fuel efficiency will plummet significantly.

Transmission issues

If your car develops a transmission fluid leak, your vehicle will begin to rev at higher RPMs due to the torque converter or gearbox band slipping. Over time, this can cause you to wear down your transmission.

The majority of the issues we’ve discussed so far are minor in nature. You won’t have to spend a fortune to get them fixed. However, when your RPM varies while accelerating, you may have a more serious problem on your hands than you realize. There are several various severe engine issues that can result in irregular RPMs.

There could be an issue with your engine’s combustion process. There might also be a problem with the engine’s capability to distribute power to the rest of the vehicle. Whatever the situation, automobile issues should not be taken lightly. They’re almost always going to result in your check engine light illuminating and staying on until you get them fixed.

What to do when the RPM fluctuates while accelerating in your car

When your RPM fluctuates while you’re accelerating, you should consider taking it to a mechanic right away. Your tachometer is going to tell you that there’s a problem brewing beneath the surface of your engine. You’ll want to find out what the trouble is and how to fix it as soon as possible so it doesn’t get any worse.

In many circumstances, all you’ll have to do is swap out your old spark plugs for some new ones. This is a quick remedy that will bring your RPM back under control. However, if you have more serious engine issues, you’ll need to consider what you want to do next. If you intend on keeping your car, you may decide it’s time to make engine repairs; however, you have the option of selling it before having to deal with expensive repairs. Regardless of the decision, whether it’s repairing or getting rid of your vehicle, you’ll want something done to it in order to avoid putting yourself in a potentially dangerous position.

FAQs

Can low RPM damage engine?

No, not under normal circumstances. When your engine speed (RPM) is low, it takes a lot more work to get the car up to speed. Engine temperature will rise, and cylinder temperature will rise as a result of this. Low RPMs are okay if you’re just cruising or slowing down, but when you accelerate, they give your engine a gearing disadvantage. This is where engine damage could begin.

What is the RPM range for an automatic transmission?

The RPM range varies from vehicle to vehicle and also depends on the type of transmission. When shifting gears, the RPM should be about 1200 – 1800.

What RPM is considered lugging?

If you press the gas pedal and don’t immediately accelerate, you’re lugging the engine. If you’re in 5th at 2,500 RPM traveling 40 mph, then you try accelerating, that’s lugging the engine. It’s the same if you’re in 2nd at 1,800 RPM going 10 MPH and attempt to increase speed. Of course, RPM varies depending on the car.

Why is my car rpm fluctuating?

There are a number of reasons why your car may fluctuate while you’re accelerating. Spark plugs have a limited lifespan so after so many miles, they begin to wear out and produce less power. Dirty fuel injectors can also contribute to RPM issues. In some cases, other causes such as low air pressure will result in the problem.

What does it mean when my RPM goes up and down?

When your RPM goes up and down, there are several reasons why. If you notice that it’s just while accelerating or just while idling, then you’ll probably have to replace either the fuel pump or the air filter. If it happens during both acceleration and idling, an issue with your idle control valve is likely. As always, if you notice anything out of the ordinary, make sure to have it checked by a professional.

Final Thoughts

If you’re unsure what to do when your RPM fluctuates while accelerating, then it’s time to take action. Your engine is sending warning signs that something isn’t right. It could be as simple as changing out old spark plugs or replacing an air filter, but more serious problems may need immediate attention so don’t delay! If you decide not to repair the vehicle, at least make sure you get rid of it before any major damage occurs. Whatever decision you end up making, always consult a professional beforehand for help with diagnosing the problem and coming up with a solution that will work best for both your wallet and safety concerns.

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