Top 6 Causes of a Car That Won’t Accelerate

Last Updated on March 9, 2021

The symptoms of a car not accelerating like it used to can occur on many high mileage vehicles. A driver might not notice these signs in normal day to day driving but they become abundantly clear when driving up a steep hill or when quickly trying to accelerate into fast moving traffic.

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It is in those situations that drivers will come to notice the obvious slow acceleration and the fact that the engine of their vehicle is struggling to keep up.

Read also: Symptoms of a Faulty Speed Sensor in Your Vehicle

Common Causes of Car That Won’t Properly Accelerate

This is a common problem in high mileage vehicles but there are no serious or immediate concerns regarding major engine problems. Some of the causes are actually minor and should be checked first in order to locate the issue and possibly fix it as well. Here are some of the most common causes:

#1 – Mass Air Flow Sensor Clogged or Malfunctioned

MAF sensor

The mass air flow sensor (or meter) is located and attached to the inlet air cleaner. Since the function of the air flow sensor is to measure air mass that is flowing into air intake, a clogged or bad mass air flow sensor could send the wrong data to the engine ECU for calculating the air fuel mixture.

A very symptom of an air flow meter malfunction is car that won’t accelerate correctly.

#2 – Oxygen Sensor Malfunction

oxygen sensor

An oxygen sensor is device whose function is to monitor the exhaust emissions of the vehicle so that it can analyze the air-fuel ratio going through the engine of that vehicle.

To make a long story short, a car needs a proper amount of fuel in order for the fuel to burn properly in the combustion cylinders so that it may run smoothly and may accelerate as required.

This sensor sends the information about the amount of fuel being used to the computer unit of the engine and if this sensor get damaged, then the engine of that vehicle will have no idea what ratio of air-fuel mixture to use which may result in a fuel rich mixture.

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

#3 – Malfunction of TPS

TPS sensor

The basic principle of the throttle position sensor (TPS) is to detect the throttle valve opening angle which is controlled by accelerator pedal. Then the TPS will send this data to the ECU.

If the TPS malfunctions, the engine speed cannot be controlled by the accelerator pedal and engine speed will increase or decrease without any press or depress the pedal.

#4 – Dirty or Clogged Fuel Filter

fuel filter

A dirty or clogged fuel filter is another reason for a car not accelerating like it’s supposed to when required to do so.

With a dirty fuel filter, the engine won’t be getting enough fuel which means that the vehicle won’t be giving the acceleration performance that it should. Replace the fuel filter as soon as possible.

#5 – Clogged or Dirty Air Filters

dirty air filter

Just like a fuel filter provides the engine with the clean fuel, an air filter provides the engine of a vehicle with clean air to be used in the air-fuel mixture which will be sent to the combustion chambers to burn.

If an air filter is clogged, then the engine won’t get the right air-fuel mixture resulting in slow acceleration. Replace the air filter as soon as possible.

#6 – Timing Belt

bad timing belt

This component is as it sounds. The timing belt is something like a VIP in the list key of components of an engine. If this belt is off even by 1 tooth, it may cause some pretty notable acceleration problems.

However the list of causes of poor acceleration does not end here. Other culprits behind slow acceleration may include a slipping clutch, the transmission system itself, or an unexpected or unrelated problem which may surprise even veteran mechanics.

If you’re not comfortable troubleshooting a car that won’t accelerate, I recommend taking the vehicle to a reliable mechanic and let him give it a full checkup. This will allow him to properly diagnose the issue and recommend a suggested fix.


331 thoughts on “Top 6 Causes of a Car That Won’t Accelerate”

  1. 2009 model, Mazda 3 car in UAE. After one hour running the car suddenly not taking speed and this happened twice in summer peak time. Mechanic checked and told no issue found.

  2. Hi, my car Honda accord 2007 189k miles. Recently, the car can’t accelerate after stopping at the intersection. At that moment, the normal light and several other lights appear on the dashboard but the engine doesn’t run at all. I press the pedal but there is no sound, like completely shut down already but still has light. When I shut down the car and start the engine again, the car works normally. Is this cause by the alternator or anything else. Hope to get help from experts from you guys. Thank you!

      • Al the lights like when I first turn the key ignited, but then I shut down the car and start it again, it worked like normal so I’m not sure if a part of my car failing or not. I heard that could be caused by the alternator. Have you heard about this situation happening on old cars?

        • When you first turn the key, it’s normal for all lights to illuminate. This is a systems check to let you know that all lamps are working as expected. Is this what you’re referring to?

  3. hello.this is also the prblm of my hard to reach 80 to 100kph.maybe i need to bring the car to the shop to avoid more problem


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