- It can be difficult to determine why your car doesn’t accelerate properly.
- A few possible causes include problems with the fuel and air delivery problems, exhaust restrictions, mechanical engine problems.
- If your vehicle stops accelerating properly, consult a licensed mechanic immediately.
You know there’s a problem when your car refuses to accelerate or accelerates poorly. Unfortunately, determining what that problem might be can be challenging—sometimes, even for professionals.
Anything from a faulty sensor to a slipping automatic transmission can prevent your vehicle from accelerating properly, as we’ll discuss below.
Why Won’t My Car Accelerate Properly? 8 Common Causes
Here’s some bad news: There isn’t a one-size-fits-all answer as to why your car might not be accelerating as it should. To figure out the root cause of the problem, you (or your mechanic) will need to do some troubleshooting. It’s important to consult a repair manual or repair database to determine the correct diagnostic procedure for your application.
Usually, you’ll find one or more of the following issues to be the root cause of poor acceleration:
Fuel and Air Delivery Problems
Your car’s engine needs a precise mixture of air and fuel to run properly. Poor acceleration can result from an engine that’s running lean (not enough fuel). Similarly, a lack of airflow can also prevent the engine from accelerating as it should.
Some of the most common causes of fuel and air delivery issues include:
- A weak fuel pump
- An obstructed fuel filter
- A faulty fuel pressure regulator
- Restricted fuel injectors
- A dirty or failed throttle body
- A collapsed air intake or severely restricted air filter
The exhaust system routes exhaust gases away from the engine and out the vehicle’s tailpipe.
If the exhaust system somehow becomes obstructed, excessive backpressure is created, and exhaust gases can get pushed back into the engine through the valves. The result is an engine that can’t breathe properly, causing a lack of acceleration.
Some of the most common causes of a restricted exhaust include:
Engine Mechanical Problems
A gas-powered internal combustion engine needs three primary ingredients to run: an air-fuel mixture, spark, and compression. Simply put, compression is the pressure created inside each of the engine’s cylinders. The pressure raises the temperature of the air-fuel mixture and helps to atomize the fuel so that the mixture is easier for the spark plug to ignite.
Low compression while running can cause poor acceleration. Some of the most common engine mechanical problems that result in low compression include:
- Worn/damaged piston rings, pistons, and cylinder walls
- Valve and valve train problems
- Faulty head gasket
- Issues with the timing belt or timing chain
If your car won’t accelerate, but the RPMs go up, then it might be because of a faulty transmission. Your car’s transmission—a complex assembly with many internal components—manipulates rotational force from the engine and transfers that force to the drive wheels. Internal automatic transmission problems (or manual transmission clutch problems) often result in “slippage” where engine RPMs increase, but vehicle speed does not. Also, a faulty automatic transmission torque converter can cause poor acceleration from a stop.
Some of the most common transmission-related problems that can lead to a loss of acceleration include:
- Internal automatic transmission failure
- Torque converter failure (automatic transmissions)
- Worn clutch (manual transmissions)
Ignition System Problems
The ignition system is responsible for igniting the air-fuel mixture inside the engine to create the energy needed to propel your car down the road. Problems with the ignition system will often cause the engine to misfire and hesitate under load, resulting in poor acceleration.
Common ignition system issues include:
- Worn-out spark plugs
- A faulty ignition coil
- Damaged or worn spark plug wires
- An issue with the distributor
- A bad ignition control module
Sensor and Module Problems
Your car’s engine sensors provide data to a computer, which is often referred to as the powertrain control module (PCM). The PCM then uses that information to control output devices, such as the ignition coils and fuel injectors.
All of the electronics (sensors, modules, etc.) that govern the engine are connected by circuitry. Furthermore, the PCM communicates with other modules over a data network to ensure the vehicle runs smoothly.
Common problems that can result in poor acceleration include:
- A failed sensor (e.g., mass airflow or throttle position sensor)
- An issue with the powertrain control module
- Circuit problems, such as damaged wires and loose connections
- Data network problems
Problems with Other Engine Management Systems and Components
But wait—that’s not all. There are additional engine management systems and components that can also lead to poor acceleration. Some of the most common include:
- Problems with the variable valve timing (VVT) system
- Problems with the electronic throttle actuator (TAC) system
- Problems with the cylinder deactivation system
- Problems with the turbocharger and related components
Vehicle Stuck in Limp Mode
On some models, certain problems (often, one or more of the issues listed above) will result in the vehicle going into a fail-safe or “limp mode”.
In limp mode, performance is intentionally limited to prevent additional damage to the vehicle and/or protect the occupants inside. The criteria for entering limp mode will depend on the year, make, and model of the vehicle.
Vacuum Hose Problems
If your car won’t accelerate past 60, then you might be dealing with a vacuum hose leak. This can be a bit tricky to diagnose because there are several vacuum hoses in your engine bay, and each one plays an important role in transporting air and fuel to and from the engine.
In some cases, one of these hoses might tear, messing with the air-fuel ratio in your engine. As your engine loses power, your car struggles to accelerate even as you step on the gas.
Oxygen Sensor Problems
A dirty oxygen sensor might be the reason why your car is struggling to accelerate and why your check engine light is on.
Your oxygen (O2) sensor helps monitor the air-fuel ratio in your engine by measuring the oxygen levels present in the exhaust. So if it’s clogged or broken, you can say goodbye to a well-functioning engine, and say hello to a car constantly struggling to pick up speed.
What to Do if Your Car Suddenly Stops Accelerating Properly?
A car that isn’t accelerating properly should be fixed right away. As we discussed, a wide range of problems can result in poor acceleration. So, if you have a lot of automotive knowledge, you might be able to diagnose and fix the problem yourself. Otherwise, it’s best to let a professional handle the repair.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.