Car Won’t Go Over 20 mph? Here’s Why

Usually, when you hit your car’s gas pedal, it is expected that your car should move in proportion to the amount of pressure you have applied to it. But when you add pressure and your vehicle accelerates slowly, then it shows there is an issue with your vehicle and you would need to find out what the problem could be.  

There are several reasons your car won’t go over 20 mph. And in this post, we will be looking at some of these issues.

car wont go over 20mph

Some Major Reasons Why Your Car Refuses to Go Over 20 mph

1. A Clogged Mass Air Flow Sensor

A mass air flow sensor is one of the key components of the electronic fuel injection system in your car. It is responsible for detecting the flow of air moving into the air intake of your car, and it is positioned and connected to the input air cleaner. 

When your car’s MAF sensor is blocked, it won’t be able to detect the correct data to your car’s ECU for computing the air-fuel mixture, and this can affect the speed of your car. You can check out this post to learn the steps on how to trick a mass air flow sensor.

2. Faulty Oxygen Sensor

Your car needs the proper amount of fuel for the fuel to burn properly in the combustion cylinders so that it may run smoothly and may accelerate as required.

The sensor sends information to the computer unit of the engine about the amount of fuel being used. Therefore, when it gets damaged, the engine of your car will have no idea of the ratio of air-to-fuel mixture to use, which may result in a fuel-rich mixture. 

This can cause the slow acceleration of your vehicle even with the accelerator pedal completely pressed, making it unreliable when it’s needed.

3. Faulty TPS

If your Throttle Position Sensor (TPS) malfunctions, then your car’s engine speed cannot be controlled by the accelerator pedal, and the engine speed will increase or decrease without any pressing or depressing of the pedal. 

If the TPS can not accurately read the throttle position, it will send misinformation to the ECU, and this will certainly affect the movement of your car.

4. Worn-out Timing Belt

A worn-out timing belt can reduce your car’s power, thereby affecting its movement. A timing belt is important for keeping internal combustion engines running. 

Therefore, when there is an issue with it, your car will experience slow acceleration. And it will require you to take it to the mechanic for it to be fixed because it needs to be done by a professional.

5. Inadequate Or Bad Fuel In The Tank

Driving on an almost empty tank can also contribute to why your car won’t go over 20 mph. This is because a nearly empty fuel tank lacks the energy required to accelerate your car. 

And also, if the gas you buy for your car contains dirt or is bad fuel, it can result in serious problems in the car. However, to correct this situation, you will need to replenish the tank with the appropriate fuel.

6. Bad Spark Plugs 

Dirty spark plugs are another factor that can affect the speed of your car. This is because plugs cease to operate properly when they’re dirty, and it will cause the engine to run rough, lack power, use more fuel, or even not run at all. 

If a spark hits a cylinder at the wrong time, it will not do anything for your vehicle. Enough misfires can cause severe acceleration issues.

7.  A Clogged Fuel Injector

Another common reason why your car won’t go over 20 mph is a dirty fuel injector. When your fuel injector is dirty, it will result in poor fuel flow in your car, and I’m sure you know that you need enough fuel to have a fast and smooth ride. 

If this is the situation with your car, you might be able to fix it by adding a fuel injector cleaning additive to your gas tank.

8. Compression Issues

The vacuum lines that run throughout your car’s engine help transfer air and fuel to where they are needed for your car to function properly. 

If the compressor or any of the vacuum lines are damaged, there is no way your car will function properly, and this will certainly affect the movement of your car. At this point, you will need to get a mechanic to diagnose the problem and replace any defective parts.

9. A Failed Clutch

When your car’s clutch is unable to correctly engage transmission fluid with the engine, it will cause acceleration problems. 

If your vehicle’s speed varies without you accelerating or decelerating, it might be due to low transmission fluid levels or a malfunctioning clutch, and you will need to take it to a professional to get it fixed.

10. Limp Mode 

If your automobile does not accelerate over 20 miles per hour, it may have entered “limp mode,” which is sometimes referred to as “limp home mode.” It is a vehicle safety feature that activates when the engine or transmission control unit detects a failure. 

It serves as a preservation feature, and when it is activated, your car moves at a slow speed. 

Limp Mode can be caused by a variety of factors, most of which should be investigated by a qualified mechanic. And its purpose is to get you home, to a repair shop, or off the road safely without ruining your engine. 

Related Post: Car Overheating Then Going Back To Normal


For your car to go over 20 mph, every part that contributes to achieving a smooth ride must be functioning properly. And in this post, we have mentioned some of the factors that could be the reason why your car can’t go at the speed you want it to go. 

However, the list does not end here, which is why I would also recommend you take the vehicle to a reliable mechanic and let him give it a full checkup. This is because most of them will require a skilled mechanic to test for and fix.