Car Won’t Accelerate But RPMs Go Up: 10 Potential Causes

One of the most common vehicle problems is when a car won’t accelerate but the RPMs go up. This can be a very frustrating issue to have, as you may feel like you’re in a car that’s stuck in a rut, unable to get up to speed.

In this guide, we’ll delve deeper into this problem and try to understand why it happens. It is important to figure out the root cause of the car accelerating problem so that it can be fixed.

So, why the car won’t accelerate but RPMs go up? The most common cause of a car not accelerating but the RPMs going up is a transmission issue. This can be due to slipping clutch bands, which can cause the car to struggle to switch gears and therefore not accelerate as it should. Moreover, if your car won’t accelerate but the RPMs go up, the engine may be misfiring. This means that the spark plugs are not firing correctly, which can lead to a loss of power. Other possible causes of car not accelerating with RPMs include vacuum leaks, a fuel filter blockage, a faulty MAF sensor, clogged air filter, bad fuel pressure regulator, dirty throttle body, clogged fuel injectors and a faulty ignition coil.

If you prefer a brief overview instead of reading the entire article, here is a summary table to quickly gather the information:

Causes of car won’t accelerate but RPMs go up	Description
Transmission Slipping	Worn clutch bands or low transmission fluid can cause gears not to engage properly, leading to RPMs rising without acceleration.
Bad MAF/MAP Sensor	Faulty MAF or MAP sensor can provide incorrect air flow data to the engine computer, resulting in improper fuel delivery and acceleration issues.
Dirty Throttle Body	Carbon buildup on the throttle body can restrict air flow into the engine, limiting power and acceleration.
Clogged Fuel Injectors	Dirty or clogged injectors prevent proper fuel delivery, causing engine power loss.
Fouled Spark Plugs	Residue buildup on spark plugs prevents them from sparking properly, reducing combustion efficiency.
Vacuum Leaks	Air leaks in the intake system cause incorrect air/fuel mixture, making the engine run lean and lose power.
Dirty Air Filter	Clogged air filter restricts air flow to the engine, reducing power output and acceleration.
Bad Fuel Pressure Regulator	Improper fuel pressure caused by a faulty regulator affects performance and acceleration.
Bad Oxygen Sensor	Faulty oxygen sensor provides inaccurate data to the computer, causing acceleration issues.
EVAP System Leak	Stuck open purge valve feeds too much fuel vapor into the engine, disturbing air/fuel ratio.

Bonus Read: Car revving on its own

What Exactly Is The RPM In Cars?

The RPM stands for rotations per minute, which is a measure of how fast the engine is running. In other words, it measures the number of times the engine crankshaft can rotate in a minute.

This rate is determined by how fast the pistons are moving up and down in the cylinders. The higher the RPM, the more power an engine can generate. 

The RPM gauge on your car’s dashboard shows you the current speed at which the engine is running.

If the needle is pointing to the left, it means that the engine is running at a lower RPM, while if the needle is pointing to the right, it means that the engine is running at a higher RPM. 

RPM is also an important factor when it comes to fuel efficiency. The higher the RPM, the more fuel the engine will use.

So, if you’re trying to accelerate quickly, you’ll need to press the gas pedal harder and increase the RPM. Again, this means that you’ll be using more fuel.

If you notice that the RPMs are running high without you pressing the gas pedal, it could be a sign that something’s wrong with your car. It could be a sign of a vacuum leak, an air filter that needs to be changed, or a faulty spark plug.

Therefore, drivers should pay attention to the RPM gauge and make sure they are driving at a speed that is comfortable for them and their car. 

Another thing you should note is that there is a difference between a vehicle’s speed and its engine’s RPM. If the engine’s RPM increase, that doesn’t mean that your vehicle will also move at high speed. The vehicle’s speed is a measure of the wheel’s speed while engine RPM is a measure of the crankshaft speed.

The engine’s RPM is only directly related to the power output. If your car is in a lower gear, your vehicle will produce higher torque. This is required when you’re are towing. If you shift to higher gears, the engine’s RPM will translate to the vehicle’s speed. 

In short, it is the transmission system of a vehicle that may limit how fast the vehicle can go, even if the engine has a high RPM.

Why Is It Important to Know Your Engine’s RPM?

Knowing your car’s RPM helps you to keep your car running smoothly and efficiently. When a car is in idle, the RPM is usually between 600 to 1000. When the car accelerates, the RPM increases, depending on the car’s power. 

Knowing your car’s RPM can also give you an indication of its fuel efficiency. A car with a higher RPM will typically use more fuel than a car with a lower RPM. By knowing your car’s RPM, you can adjust your driving habits accordingly to maximize fuel efficiency and save money at the pump. 

Maintaining your car’s RPM is also important for its performance. When the RPM is too high, it can cause your engine to overwork, leading to decreased fuel efficiency and increased wear and tear. On the other hand, when the RPM is too low, it can cause your car to struggle and perform poorly. Knowing your car’s RPM can help you make sure it’s running at its best. 

Why Do Some Cars Have Higher RPM Than Others?

It can be a bit confusing, especially if you don’t know much about cars. The truth is, there are a few different factors that can make this happen. One of the most common is engine size.

Smaller engines need to spin faster in order to generate the same amount of power as larger engines. That’s why cars with smaller engines tend to have higher RPMs. 

This is because small engines have small engine displacement as compared to large engines. In small engines, the piston travels a small distance from bottom to top in the engine cylinder. So, a small engine has to spin faster to generate the same power as a large engine does at a lesser RPM.

First Thing To Do When Car Is Not Accelerating With RPMs

You should first check if the check engine light illuminates on the dashboard. Usually, when there is any fault in the engine or transmission, the engine control module turns on the check engine light and stores the OBD2 trouble code. 

Sometimes, check engine light turns off automatically, but you have to plug in this OBD2 scan tool to check for trouble codes stored in the engine computer’s memory.

That step makes troubleshooting quite easy for you as you won’t have to check each component of the engine to fix the vehicle acceleration issue.

What Exactly Is Efficient Combustion In Engine?

The ability of an engine to burn its fuel efficiently largely depends on the ratio of air to fuel.

When the air-fuel ratio is correct, the combustion process is more efficient, resulting in improved power, smooth acceleration and fuel economy.

For efficient combustion to happen, the air-fuel ratio must be kept as close as possible to 14.7 parts air to 1 part fuel.

Modern engines have sensors that send signals to the engine’s computer to adjust the amount of fuel in response to the intake air volume so that efficient combustion takes place.

Even if engine sensors are working properly, another thing that affects combustion is engine misfiring. 

This usually happens because of clogged fuel injectors, dirty air filters, and fouled spark plugs. These components do not play role in adjusting the air-fuel ratio. But, they still have a substantial impact on combustion efficiency.

Causes Of Car Won’t Accelerate But RPMs Go Up

Here are the causes of car won’t accelerate but RPMs go up:

1. Transmission Slipping

If your car has an automatic transmission and is not accelerating when RPMs go up, the chances are that gears are not shifting in your automatic transmission.

The automatic transmission consists of the following components:

• Torque converter
• Solenoid valves
• Valve body
• Transmission fluid
• Clutch bands

The torque converter is a fluid coupling device that converts engine torque to the drive shaft of the car. This helps to transfer power from the engine to the wheels. The torque converter is filled with transmission fluid, which helps to reduce friction and ensure a smooth operation.

The solenoid valves in automatic transmission are the control valves that direct the flow of transmission fluid.

They control the shifting of gears, depending on the amount of acceleration or deceleration. The solenoid valves are connected to the valve body, which consists of several small passages that control the movement of the fluid. 

The pressure control solenoid maintains the desired pressure of oil in the valve body. Shift control solenoids are open and closed to direct the oil through the channels in the valve to shift the gears.

In the below figure, I have shown the valve body and solenoids for Hydra-Matic 4L65-E:

1. Transmission fluid pressure switch
2. 1-2 shift control solenoid
3. 2-3 shift control solenoid
4. Pressure control solenoid 

The clutch bands are responsible for shifting the gears, and they are connected to the valve body. Transmission fluid, after passing through control solenoids, exerts hydraulic pressure to clutch bands to engage and disengage them.

How to spot?

The main reason for transmission slipping is the low or bad transmission fluid. Like engine oil, transmission fluid has also a dipstick. You should make sure that the transmission fluid level is between high and low marks on the dipstick.

To check the level of transmission fluid:

• Park a car on level ground.
• Start the car to warm up the engine to an operating temperature as the minimum and maximum marks on the transmission oil dipstick are based on the transmission temperature of around 90ºC to 100ºC. The engine should not be run for more than 90 seconds to warm it up.
• With the engine running, depress the brake pedal and place the gear lever in each gear position, holding for approximately 5 seconds in each position. Then, put the gear lever in PARK.
• Turn off the engine.
• Remove the dipstick from the transmission and wipe it with a clean cloth.
• Insert the transmission dipstick all the way into the transmission.
• Remove the dipstick and check the transmission fluid level.
• If the level of transmission fluid is below the lower mark on the dipstick, it means that the transmission oil level is low.

Note: If a car has been in use for a long time under different driving conditions – such as high-speed highways, city streets, hot days, or even towing a trailer – it is necessary for its transmission fluid to cool down to 90ºC for an accurate reading.

If the transmission fluid has a dark color, it means that you should flush the transmission.

Next, you should check the control solenoids in the valve body. You can watch the below youtube video to test the solenoids of an automatic transmission system:

Won-out clutch pads also cause clutch slipping which results in the car not accelerating but RPMs going up.

When it comes to clutches, the abrasive material found in the pads is essential for providing the grip necessary to apply pressure on the different gear sets within the drivetrain. Over time, however, when the pads become worn out, their grip begins to deteriorate, leading to the clutch slipping and no longer engaging the gear. 

2. Bad MAF/MAP Sensor

After you have confirmed that your automatic transmission is completely fine, and is not causing acceleration issues in your car, it’s now time to check all those components that affect the combustion efficiency of the fuel in your engine. One of those components is either MAF or MAP sensor.

Some engines have MAF (Mass airflow sensor) and some have MAP (Manifold Air Pressure) sensor. I have Toyota Vitz 2018 model. It has a MAP sensor. So, you should check the owner’s manual of your vehicle.

The MAF sensor measures the amount of air entering your engine. It does this by using a heated wire that measures the amount of air passing through the intake. This helps the engine’s computer determine the amount of fuel to inject into the cylinders. The MAF sensor is usually located after the air filter and before the throttle body.

MAP sensor measures the pressure in the intake manifold. This helps the computer determine the load on the engine and the amount of fuel that needs to be injected. The MAP sensor is usually located on the intake manifold.

How to spot?

MAP sensor sends voltage signals based on changes in the vacuum in the intake manifold. When the engine is idle, the vacuum is maximum. 

So, the voltage shown by the MAP sensor should be minimum at that point. As you press the gas pedal, the vacuum decreases and the voltage reading sent by the MAP sensor also increases.

Before testing the MAP sensor, make sure that the vacuum hose attached to it does not have any dips or sags. Furthermore, there should not be any moisture inside the vacuum hose.

Now, turn on the ignition key and keep the engine off. Attach the probe of the multimeter with the signal wire of the MAP sensor. It should read around 4 volts.

Now, start the engine, and operate it until normal operating temperature is achieved. Read the voltage of the MAP sensor at the idle speed of the engine using the multimeter, It should be around 1.6V.

Now, press on the accelerator pedal and note the voltage of the MAP sensor. If the voltage does not increase, it means the MAP sensor is bad.

You should have access to the specifications of the MAP sensor installed in your engine to get an idea of the correct range of voltages.

Experts do not recommend cleaning the MAP sensor. So, you have to replace it.

MAF sensor also sends voltage output to the ECM. As the mass flow rate of air through the MAF sensor increases, voltage output also increases. 

As you press the gas pedal, more air passed through the MAF sensor. As a result, voltage output increases. At idle, the voltage should be less than 1.0V. As you increase RPM, the voltage output by the MAF sensor increases from 1.0V to 1.7V. 

If the voltage of the MAF sensor is fluctuating, you can clean that heated element of the MAF sensor using this cleaner. Be sure to never touch that wire of the MAF sensor. Let it dry completely before re-installing the sensor.

Here is a short Youtube video explaining how to clean the MAF sensor.

3. Dirty Throttle Body

Most of the sluggish engine problems are solved by cleaning a dirty throttle body. A throttle body consists of a butterfly valve that controls the amount of air that enters the engine. It’s connected to the accelerator pedal and is responsible for controlling the engine speed. When the accelerator pedal is pressed, the throttle body opens, allowing more air to enter the engine. This increases the engine speed and allows the car to accelerate.

It is a common issue for the throttle body to become dirty over time, which can cause your car to not accelerate properly.

Signs of a dirty throttle body include a decrease in engine performance, poor fuel economy, and the RPMs going up when you try to accelerate but the car not responding.

If the throttle body is dirty, it can cause the engine to not get enough air, which can lead to the RPMs going up when you press the accelerator but the car not responding.

How to spot?

The throttle body can get dirty over time due to a buildup of dirt, debris, and carbon deposits.

When the throttle body becomes dirty, it restricts the movement of the valve, making it difficult for it to move freely under the action of the spring force.

As a result, the engine won’t be able to take in as much air as it needs to, and the vehicle won’t be able to accelerate properly. 

In short, the throttle butterfly valve should move open and to the closed position under the normal spring pressure without binding.

You should use this throttle body cleaner to clean the throttle body. Remove the throttle body from the engine and scrub it with a soft piece of rag after spraying the throttle body cleaner.

You can also use this brush kit to gently dislodge the dirt inside the throttle body. Make sure to spray the throttle body cleaner by staying 10-12 inches away from the throttle body. 

4. Clogged Fuel Injectors

Fuel injectors are small nozzles in the fuel system that spray fuel into the engine. They are responsible for providing the right amount of fuel to the engine at the right time.

When the fuel injectors become clogged, they are unable to deliver the proper amount of fuel to the engine. This can cause the engine to run lean, meaning there is not enough fuel to properly combust.

When this happens, the engine will have to work harder to achieve the same power output, resulting in higher RPMs. As the engine is working at a higher RPM, it will not be able to accelerate properly. 

Also Read: Car won’t start after replacing fuel injector

The fuel injector, itself, is an electronically-operated valve that is controlled by the car’s computer. It opens and closes to precisely regulate the amount of fuel that is delivered to the engine. 

How to spot?

Fuel injectors are clogged due to carbon deposits and the accumulation of dirt around the nozzle of the fuel injectors.

A fuel injector can also become damaged due to its faulty magnetic coil. If you look at the fuel injector, you will see its two terminals. These are the endpoints of the magnetic coil of the fuel injector that carry electric current.

A fuel injector also consists of an o-ring to prevent leakage of fuel. You should check if the o-ring is damaged. Usually, the engine manufacturer has specified the part number of the O-ring to be installed on the fuel injector. Use your palm to push the o-rings until they sort of “pop” into place.

There are several methods to test a bad fuel injector. You have to check the fuel injector electrically, and also make sure it is delivering the fuel. First, you should have a multimeter and connect its probes to the terminals of the fuel injector.

Set your digital multimeter to an appropriate value on the Ohms scale according to the resistance specifications for your particular fuel injector (usually, you need to set the multimeter to read at least up to 30 Ohms).

If the resistance across terminals of the injector reads infinite resistance, it means the coil in the injector is opened. If the multimeter shows OL or very small resistance, it means that the coil in your injector has short-circuited. If it shows resistance specified in the specs of your fuel injector, it means that the coil of the fuel injector is fine.

Another test for a bad fuel injector is to observe if it is emitting a clicking noise or not. For this, you would need a long screwdriver to hear the clicking noise. Now, pull out the fuel rail. But make sure that it is connected to the fuel supply hose.

Turn the key on to prime the fuel pump and pressurize the fuel line. Now, hook the 9v or 12v battery one by one to each fuel injector and try to hear its ticking noise with a long screwdriver.

That ticking noise is basically the opening and closing of a pin in the fuel injector.

Also, see if the fuel injector is injecting fuel in a certain direction without leaking or not. If it’s leaking, you would need a new fuel injector.

You can check out the following video from 2:40 to get an idea of how to test fuel injectors.

Apart from the above experiments, check these things on the fuel injector:

• Look for burrs on the injector inlet
• Check nozzle holes for hole erosion or plugging
• Inspect the end of the nozzle for burrs or rough machine marks
• Look for cracks at the nozzle end

5. Fouled Spark Plugs

When a car won’t accelerate but the RPMs go up, it can be an indication that something is wrong with your spark plugs.

Fouled spark plugs can occur when a spark plug becomes coated in a layer of residue. This could be caused by a number of different factors, including but not limited to oil, fuel, or carbon deposits.

When a spark plug becomes fouled, it can prevent a spark from properly igniting the fuel in the engine, and this can cause the car to not accelerate properly. 

You can read this PDF to learn about signs of fouled spark plugs.

Another type of fouling is caused by a phenomenon known as “corona stains.” This occurs when the spark plug is exposed to a high voltage and the electrical charge is conducted away from the spark plug.

This can cause a light-brown stain around the porcelain body (white-colored part) of the spark plug, which can reduce the spark plug’s efficiency and cause engine misfires. 

How to spot?

The most common cause of spark plug fouling is a fuel mixture that is too rich. This is when the ratio of fuel to air has too much fuel. This creates a heavy fuel vapor that can coat the spark plug and prevent it from firing correctly.

When fuel injectors are bad, they can inject too much fuel inside the engine’s cylinder which can foul spark plugs.

Oil or dirt particles can also foul spark plugs. This can happen when the air filter or air intake is dirty, allowing dirt or oil to enter the combustion chamber.

In addition, if the engine’s oil level is too high, oil can be forced into the cylinder, coating the spark plugs. It’s important to regularly check the air filter and oil level to ensure that the spark plugs aren’t becoming fouled. 

In order to properly diagnose the problem, it is important to take a look at the spark plugs. If they are covered in a layer of residue, then it is likely that they are fouled. You can use spark plug socket to remove the spark plug and visually inspect it.

The general consensus is to replace spark plugs rather than clean them. Cleaning spark plugs is an outdated practice that went out with cleaning points and replacing condensers. Once a plug gets fouled to the point of misfiring, cleaning them will not bring them back to good performance.

Also Read: My car sometimes start and sometimes it doesn’t

6. Vacuum Leaks

A vacuum leak is characterized by the suction of unmetered air in the engine’s air intake system. Any air that enters the engine without passing through the MAF/MAP sensor will be defined as a vacuum leak.

This is because MAF/MAP sensor couldn’t detect that amount of air to send signals to the ECM so that it could adjust the fuel accordingly. As a result, the air-fuel ratio is disturbed and the engine runs lean.

When the air-fuel ratio is not balanced, the engine will not be able to maintain a steady RPM when the accelerator is pressed.

Instead, the RPMs will increase as the engine struggles to make up for the missing fuel. This is why your car won’t accelerate but RPMs go up. 

How to spot?

Here is how to spot vacuum leaks in engine:

1. Worn or cracked vacuum hoses: Vacuum hoses are the tubes in the engine air intake system that help to create the vacuum. If these hoses become worn or cracked, it can cause a vacuum leak.
2. Faulty or damaged intake manifold gasket: The intake manifold gasket seals the engine air intake system and helps to create a vacuum. If this gasket is faulty or damaged, it can cause a vacuum leak.
3. Defective intake valves: Intake valves are the valves that open and close in the engine cylinder to create the vacuum. If these valves are defective, they may not be able to create a vacuum, which can lead to a vacuum leak.
4. Faulty PCV valve: The PCV (positive crankcase ventilation) valve is responsible for controlling the flow of air and fuel in the engine. If this valve is faulty, it can cause a vacuum leak.

You can use a carb cleaner to detect vacuum leaks in the engine. You can watch the below Youtube video for a better understanding.

7. Dirty Engine Air Filter

The engine air filter is designed to trap dirt and other contaminants from the air before it gets into the engine. As the air filter gets older and dirtier, it becomes less effective at trapping contaminants and allowing air to flow freely. 

When the engine air filter is dirty, it restricts the amount of air flowing into the engine. This can cause the car to not accelerate but the RPMs to go up.

The reason for this is that the air filter is unable to filter out all the dirt and debris in the air, which is needed for the car to burn fuel efficiently.

The lack of airflow to the engine results in the car not being able to reach its optimum performance levels. The RPMs go up as the engine is trying to compensate for the lack of airflow and is working hard to try and get the car to accelerate. 

Generally, engine air filters should be changed every 12,000 to 15,000 miles. It’s also good practice to change the air filter when you take your car to the mechanic for an oil change.

8. Bad Fuel Pressure Regulator

The main function of the Fuel Pressure Regulator (FPR) is to maintain a steady pressure in the fuel system. This pressure is important for the car’s performance and fuel economy. 

If the fuel pressure regulator fails, the fuel pressure can become too high or too low, and this can cause a number of different problems.

When a car has a bad FPR, the engine will still run, but the car will not accelerate properly. This is because the fuel pressure is not at the correct level, so the engine is not getting the proper amount of fuel. 

Keep in mind that Gasoline Direct Injection (GDI) engines have a fuel pressure sensor instead of a fuel pressure regulator. So, if your engine has GDI technology, you should check the fuel pressure sensor. This sensor measures fuel pressure inside the fuel rail and sends signals to the ECU to maintain the fuel pressure.

If you want to learn the proper functioning of a fuel pressure regulator and how it fails, you can read my guide on the symptoms of a bad fuel pressure regulator. In this guide, I have explained the proper functioning and location of a fuel pressure regulator with a schematic diagram.

Furthermore, if a throttle body is becoming dirty over and over again, it could signify that the fuel pressure regulator (FPR) is faulty. This is due to the fact that the FPR has a diaphragm, which can rupture and lead to fuel entering the throttle body. 

9. Bad Oxygen Sensor

The oxygen sensor is a vital component in a vehicle’s engine; it is responsible for monitoring the air-to-fuel ratio. It works by detecting the amount of oxygen in the exhaust.

If the oxygen sensor is malfunctioning, the engine could be running too rich or too lean, leading to damage. One of the warning signs of a damaged oxygen sensor is when the car won’t accelerate even though the RPMs are increasing. 

Your vehicle has two oxygen sensors. One is before the catalytic converter and the other is after the catalytic converter. You should check the first oxygen sensor as this one measures oxygen amount in exhaust gases to maintain the air-to-fuel ratio.

How to spot?

The voltage generated by the oxygen sensor should fluctuate within a certain range as the air-fuel ratio changes. If the oxygen sensor is not functioning properly, the voltage may not fluctuate as it should, and the engine may not run at its optimal performance. If this is the case, it is important to have the oxygen sensor checked and/or replaced by a qualified automotive technician.

For a healthy O2 sensor, the voltage should fluctuate at least once time for every two seconds. The voltage range should be between 850mV and 150mV. If the O2 sensor’s reading is stalled in position, or switches abnormally high or low, your sensor has failed.

To test the O2 sensor, you should connect the positive lead of the voltmeter to the signal wire of the O2 sensor. If the O2 sensor has two wires, connect the negative lead to the negative wire of the sensor.

10. EVAP System Is Leaking

EAVAP (Evaporative Emission System) system is responsible for controlling the emissions of fuel vapors from your car’s fuel tank and other components.

The EVAP system helps to keep fuel vapors from entering the atmosphere by venting them into the engine’s intake manifold.

The EVAP system consists of four main components: a charcoal canister, a purge valve, a vent valve, and a pressure sensor.

The charcoal canister, also known as a vapor canister, is part of the EVAP system that captures and stores fuel vapors. It is made up of two parts: an activated charcoal filter and a rubberized container.

The charcoal filter is designed to absorb fuel vapors, and the container helps keep them contained. The canister is typically mounted somewhere in the engine bay, usually near the fuel tank. 

The purge valve is part of the EVAP system that allows the stored fuel vapors to be released. It is a small, electrically operated valve that is opened and closed by the vehicle’s computer, allowing the fuel vapors to be released into the engine’s intake manifold, where they are burned, rather than released into the atmosphere.

The vent valve is part of the EVAP system responsible for allowing fresh air into the charcoal canister. The vent valve is opened all the time. It is only closed when detecting leaks in the EVAP system.

In my guide on car sputtering after getting gas, you can learn the proper working of the EVAP system with a schematic diagram.

So how does a leaking EVAP system cause a car to not accelerate but the RPMs to go up? It all has to do with a stuck open purge valve.

The purge valve is a part of the EVAP system and its job is to open when there is an excess of fuel vapors inside the fuel tank and allow fuel vapors to be pulled into the intake manifold.

When this valve sticks open, it can allow too much fuel vapor to be pulled into the intake manifold, which can cause your car to not accelerate properly.  

If you have a Ford vehicle, you can see the P1450 code on the OBD2 scan tool if the EVAP valve is bad.

You can watch the below video to test the EVAP purge valve:

Car Won’t Accelerate But RPMs Go Up: FAQs