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Why Car Won’t Accelerate


Why Car Won’t Accelerate

A car that won’t accelerate is no good to you at all. You want a car that will go. Besides the aggravation of driving at a slow speed, a non-accelerating car can also be dangerous. You will find it hard to merge into traffic when you can’t move along with the flow. 

Many reasons exist for why car won’t accelerate. The most common reason is a clogged air filter, but it could also be a bad airflow sensor, idle air control valve, hung up throttle “butterfly” valve, a bad throttle position switch,  fuel or fuel delivery issues, control sensor, spark plug issues, alternator or an emergency brake problem. 

It could also be a transmission issue or the car went into protection mode where it keeps it moving slowly until you have it checked out by a mechanic. It’s fortunate that most of these problems can be resolved by yourself or a mechanic at a fairly low price.

The article below details how you can tell which problem may be affecting your car’s acceleration.

The Most Common Problem of Air

When you have a problem with your car, the first thing to do is to look at the simplest solution first because that is probably the problem. A problem with acceleration likely means you have a dirty or clogged air filter. 

Cars need three things to work: air, gas, and fire. A lack of acceleration means there is a problem with one of those things. Keeping your air filter clean and replacing it with regular oil changes will go a long way to keeping the airflow correct and your car running smoothly. 

Checking the air filter is easy enough. All you have to do is remove the air filter cover and look. A filter that is brown, black, or dirty can be seen easily. 

You can remove the air filter and clean it as long as it’s pretty new. Replacing it will be the best choice most of the time.

Bad airflow can also be caused by other issues.

A bad airflow sensor, air control valve, or throttle butterfly valve can also contribute to improper airflow. The sensor is supposed to send a message that air is mixing properly with the fuel and a faulty one means that message isn’t sent. 

That may mean the computer slows the car down to protect the car or it just may not function properly in acceleration.

The air control valve and butterfly valve controls the amount of air mixing with the fuel. Your car will be slow to function if either of those goes bad. Another symptom of these kinds of issues is if your car shakes when it idles.

You can check the butterfly valve easily by looking at the throttle. It’s a visible piece and you should be able to tell whether it’s frozen, clogged, or dirty. 

The air control valve may be more challenging to find, depending on the make and model of your car. It could be a simple fix also as it may just be dirty or clogged and may not need replacing.

Read: When Should You Replace The Engine Air Filter?

Fuel Issues

The second part of the combustion equation is gas. Any problem with fuel moving through the car will cause acceleration problems. The most common problem relating to fuel is driving on a low gas tank. 

Driving with little gas can cause a lack of acceleration. It’s like trying to suck up the last of a soda through a straw. It takes a lot of effort on the car’s part to get to that last bit of fuel. 

Plus, things like water and trash become more prevalent as you get lower in gas. That can clog up fuel lines and cause a rough drive. 

Fuel delivery issues can include a clogged fuel pump or clogged injectors. These are pretty easy fixes as there are cleaning products that clean out these things by adding them to your gas. Another option is to fill up with a higher grade of gas once or twice to see if that cleans the pump and injectors. 

Read: How to Start a Car With a Bad Fuel Pump

Car Sensors

Sensors can do several things but some sensors check the air to fuel ratio. A faulty sensor can cause acceleration problems because it isn’t sending proper messaging to the car’s computer regarding the air-fuel mix. 

The car won’t function properly without the computer getting the right message. It will take a mechanic to check and replace sensors as the right one can be tricky to find and replace.

Fire and Power Issues: Spark Plugs

The final part of the equation to create combustion is fire. A lack of fire would point to bad spark plugs. Typically, you will notice that spark plugs are going bad when the car also misfires in addition to moving too slowly. 

Spark plugs can also arc incorrectly if the wire casings become too thin and that could be part of your problem. Checking the wires when you get your plugs replaced will keep the problem from occurring.

Read: Why Is There Oil On My Spark Plug Threads?


The alternator is an important part of the car because it converts energy to keep the battery powered. Without it, your car will run solely on the battery and the battery won’t keep recharging. This will eventually cause a decrease in power. 

Symptoms of a bad alternator will be the speed slowing, lights dimming and electrical features not working. Eventually, the car will stop due to a loss of power. 

Read: Can You Jumpstart a Car With a Bad Alternator?

Other Common Issues

Emergency Brake

It may sound silly but check to see if your emergency brake is on if your car won’t accelerate. It may not be pulled completely up but it could be pulled far enough to slow your car down. 

You will also know it’s the emergency brake if you start to smell rubber as you’re driving. 

How Do I Know It’s Not a Transmission Issue?

Transmission issues are typically showcased by only an acceleration problem. A bad transmission usually has symptoms of the car working fine until it reaches a certain speed. It may be fine after it reaches a higher speed. 

It also may jerk in the lower speeds and you’ll feel a slippage into another gear. 

Read: Why Your Car’s Transmission is Slipping & Fix

The Safety Mode

Many cars today are equipped to go into safety mode if there is something wrong with the engine. This happens automatically to protect the engine. A car going into safety mode means it will only go up to one slow speed, like 25 mph, and no more. However, it runs fine at that speed. 

You may have a dummy light that pops up indicating your car is in safety mode.

Take your car to a mechanic if doing those things doesn’t fix the problem. Most of these other problems don’t cost a lot of money to fix as long as they don’t hurt your engine or transmission. Look for the price to be $200 or less to fix any one of these issues. 


Why won’t my car go when I press the gas?

The problem is probably either a clogged fuel filter. A clogged filter will inhibit the car from performing well. Other symptoms of a clogged fuel filter is sputtering or stalls. 

Why does my car not accelerate but the RPMS are up?

This is a sign that the transmission is slipping or the gears are starting to slip. A clear sign of a transmission problem is if your engine revs up when you press the gas but the vehicle doesn’t go as fast as it should when you accelerate. 

Why does my car not accelerate but jerks?

The probably reason is you have dirty fuel injectors. This is the most common reason why a car will jerk. Dirty injectors result in your cars losing power when you press the gas pedal. There could be an engine misfire as well.

Why won’t my car go past 50 mph?

The culprit in this situation is typically a dirty or clogged fuel filter. Your car isn’t getting enough fuel at higher speeds and this can cause acceleration problems. You can also have a dirty air filter that isn’t giving your car the correct fuel-air mixture. 

Why won’t my car go faster than 25 mph?

Your vehicle may be in safety mode, commonly called “limp mode.” Cars will automatically enter this mode to protect the engine while it gets your home or to a mechanic. You must take it to a mechanic to get it out of limp mode and discover your problem. 

What are the signs of a failing transmission?

A failing transmission has some sure signs other than an acceleration problem. It will not switch gears easily and there is a burning smell. There could be noises coming from the car when it’s in neutral, fluid leaks, and the check engine light may come on.

Why does my transmission slip when I accelerate?

Gears that slip may have sustained a lot of wear and tear. They do wear out and they may be linking together correctly. This can cause for a bumpy ride as you accelerate. 

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