The symptoms that your car is not accelerating the way it used to may occur to any vehicle. You may not notice the problem on regular days along the usual routes but they become clear when you decide to drive up a steep hill or accelerate to move into the fast lane. In such situations, you may notice the slow acceleration and the engine struggling to keep up.

Your vehicle uses a complex system to move. The Causes of Car Not Accelerating When Pressing Gas can be many.   The car may not be getting the right mix of air and fuel to burn, the spark plug may not ignite at the right time, the exhaust gases may not be leaving the system correctly.

There are many sets of variables that affect the car’s optimal performance. Besides an idle car’s requirements are different from when it is accelerating. If you are driving the car in colder regions it requires more fuel as the air is denser.

The Electronic Control Module or Unit (ECM or ECU) is the brain of the vehicle. It gets a feed of inputs from various sensors in every part of the car. These feeds control the spark timing, the amount of fuel released into the system, etc. It also monitors the emission system to ensure the vehicle running in an eco-friendly manner. There are many Causes of Car Not Accelerating When Pressing Gas.

The 5 Causes of Car Not Accelerating When Pressing Gas

The major reasons your car is not accelerating are as follows;5 Causes of Car Not Accelerating When Pressing Gas in 2020

Fuel Problems

The most obvious cause of low, slow, or no acceleration may be that your car does not have enough fuel. The other reason could be that something is preventing the fuel from reaching the combustion chamber in correct quantities and air-fuel ratio.

The humble fuel filter is often overlooked. But a dirty or clogged fuel filter is a common culprit for this problem. When not serviced for a long time these filters become clogged with debris and sediment from the fuel. They should be removed, cleaned, and replaced regularly.

The hazard with dirty fuel injectors is that they can misfire or have an irregular spray due to the clogs. This affects the combustion process. The injectors are cleaned by putting fuel additives in the fuel tank.

Another reason could be a bad fuel tank. It may not be providing an adequate amount of fuel. Thus, it requires to be replaced. This happens because these pumps weaken over time especially if you drive around on an almost empty fuel tank.

The reason being that fuel pumps are cooled by the fuel while they pump it. They are submerged in the fuel that cools them by heat transfer. Thus, if there is an insufficient amount of fuel in the tank it does not cool down. This shortens the fuel pump’s life.

The other fuel issue may be the use of incorrect octane fuel or the fuel could carry contaminants such as water or dirt. This affects acceleration. The only way to remedy this is to empty the fuel tank, dry it and refill it with a higher-octane fuel.

Mechanical Problems

A car is a machine and a machine has many moving parts. The deceleration may be due to a problem in any of these moving parts.

A misaligned timing belt is a VIP on the list of mechanical parts because if it is misaligned even by one tooth and the tension is incorrect – it can cause some serious acceleration issues.

A slipping clutch or a low level of clutch fluid may be the issue. Due to these issues, the gearbox may not be able to engage correctly with the engine. A slipping clutch causes the engine speed to increase while the ground speed remains constant.5 Causes of Car Not Accelerating When Pressing Gas in 2020

The mass airflow sensor/meter is attached to the inlet air cleaner. Its function is to measure the mass of air flowing into the intake. A clogged or damaged airflow sensor can send incorrect data to the Engine Control Unit (ECU) calculating a faulty air-fuel mix leading to incorrect acceleration.

The Exhaust Gas Recirculation Valve (EGR valve) may be stuck open letting too much exhaust into the system. This throws the sensors off reducing the amount of oxygen into the cylinder that leads to less power. A closed EGR valve does not affect the power. It only affects the engine acceleration if it causes the Engine Control Unit (ECU) to place the car in a limp mode.

The oxygen sensor monitors the exhaust emissions to analyze the air-fuel ratio passing through the engine. Your car requires the right amount of fuel and the right amount of air to burn properly in the cylinders to gain proper acceleration. These sensors send information regarding fuel consumption using the computer unit in the engine. If the sensor is damaged an incorrect amount of air-fuel mix will enter the engine affecting its performance. If the fuel is too rich it may cause slow acceleration even when the pedal is floored.

The Throttle Position Sensor (TPS) detects the angle of the throttle valve opening which is controlled by the accelerator pedal. This sensor sends data to the Engine Control Unit (ECU). When this sensor malfunctions the speed of the engine cannot be controlled using the accelerator pedal. It may increase or decrease without engaging the pedal.

Besides dirty or clogged fuel filters, dirty air filters may be the cause of your car is not accelerating. Just the way your car needs clean fuel, it needs clean air free of dust and debris. The right amount of air in the fuel minus contaminants will be sent to the combustion chamber to fire the engine. Dirty air filters require to be replaced to remedy the slow acceleration.

A faulty or clogged catalytic converter leads to too much back pressure on the car’s engine. A clogged catalytic converter is dangerous as it may catch fire. Park the vehicle until it is repaired.

The car may also not accelerate because the emergency brakes are on.

Electrical Problems

If the sensors in your car do not function properly the Electronic Control Module or Unit (ECM or ECU) gets confused and responds to incorrect data leading to sluggish acceleration.

Different vehicles have diverse types of sensors. These may include the MAP sensors, Oxygen sensors, Mass Air Flow sensors, Throttle Position Sensors, Crankshaft sensors, Coolant Temperature sensors, Camshaft sensors, etc.5 Causes of Car Not Accelerating When Pressing Gas in 2020

Some cars go into a Limp Mode when a fault is detected. This fault is usually detected by an errant sensor. There may be excessive knocking in the engine or a problem in the emission control system. When the car enters this mode the check engine light turns on and the power to the engine is greatly reduced. it is best to take your car to the workshop when it enters this mode.

Ignition coils convert the low voltage from the battery into a high voltage that is needed for the little spark to jump the gap on the spark plug.

The distributor passes this voltage from the ignition coil to the spark plug. Some modern cars do not have distributors so they may or may not have this problem. A faulty ignition coil, distributor, and spark plug can cause the engine to misfire. If no spark is produced, there is no explosion. Besides the explosions have to occur at the right time with the right mix to power and accelerate the engine. Sparks at the wrong time may even harm the engine. Thus, these electrical problems need to be corrected to gain proper acceleration.

Since the timing of these combustion events and the release of the correct mix of fuel and air needs to be accurate for the car to run efficiently. The data going to the Electronic Control Module or Unit (ECM or ECU) needs to be correct. This can be achieved only by tuning the engine to the optimum values.

Air Flow Problems

The basic requirement of a combustion engine is the correct flow of air. If the air is contaminated with impurities or the airflow is restricted it results in acceleration problems.

A clogged or dirty air filter may be the cause of the deceleration. The car manufacturers recommend that these filters be replaced at regular intervals. You can check the service manual and keep records of our car maintenance. Please note – the air filter for the car cabin is a part of the HVAC system and is not the same as the engine air filter.

The body of the throttle is a tube containing a butterfly valve. It is also known as the throttle plate. This valve controls the amount of air that gets into the intake manifold. It is also connected to the inputs from the right foot. If this value is stuck in one position or there is a buildup of debris then the vehicle’s performance deteriorates and it may rough idle, too.

When driving through high-altitude places you may notice your engine lagging and struggling. This huffing and puffing may be more noticeable while driving uphill. This is due to the lack of oxygen at higher altitudes. Oxygen in the air-fuel mixture is crucial for this mix to burn efficiently and completely in the combustion chamber. As there is less oxygen at high altitudes – less oxygen than required is mixed in the air-fuel mixture 5 Causes of Car Not Accelerating When Pressing Gas in 2020causing the engine to strain.

Regular or naturally aspirated vehicles are more likely to develop these issues than the forced-induction ones like the turbo or supercharged cars. This is because their engines force air into the engine and compensate for the reduced air pressure and low concentration of oxygen in the air. In modern cars, the sensors should be able to detect this issue and suck in more air to make up for the oxygen deficit.


The car may not accelerate due to clogged or leaking hoses. Engine vacuum is the measurement of the air pressure in the intake manifold. This air pressure in the engine is relative to the atmospheric pressure.

When the throttle is closed – in the event of idling or when your foot is off the gas – the engine vacuum is maximum. In this state, the combustion cylinders are trying to pull in more air than the throttle plate lets into the intake manifold. Thus, the pressure in the intake manifold is lower than the atmospheric pressure.

When the throttle is completely open the pressure in the manifold is almost equivalent to the atmospheric pressure of this place. There is little or no vacuum in the manifold.

Super or turbo-charged vehicles may even develop a positive pressure as the supercharger or turbo pushes the compressed air into the intake manifold. This leads to the manifold having greater pressure than the ambient atmospheric pressure.

Vacuum hoses affect the behavior of many car components such as fuel pressure regulator, brake booster, EGR valve, etc. If there is a leak in these hoses the connected component will behave errantly and erratically.

The air leak in or out of the system is not measures by the Manifold Absolute Pressure (MAP) or Mass Air Flow (MAF) sensors. This throws off the vehicles’ air-fuel ratio. In supercharged vehicles, this may manifest as a boost leak. This affects the amount of air entering the fuel combustion chamber which is well below the expected volume.

A compression ratio is another crucial feature of a combustion engine. The ratio between the volume of the cylinder when the piston is at the lowest point to the volume with the piston is at the highest is the compression ratio.5 Causes of Car Not Accelerating When Pressing Gas in 2020

Higher the compression ratio the more forceful in the explosion in the cylinders. There are many reasons why the gases may leak out of the engine – this in turn – diminishes the compression ratio. A low compression ratio leads to power problems.

The most probable causes of these leaks may be worn or cracked piston rings or worn valves, valve springs, and cylinder linings. There may be a carbon build-up around the valve seats, the valve clearances may be out of specs or it may be blown head gaskets.

These worn-out components cause the combustion gases to leak out of the chamber. This reduces the compression ratio in the combustion chamber leading to lower potency of the explosion in that cylinder.


In conclusion, we have shared the list of reasons your car may not be accelerating despite pressing the gas. The reason may be the faulty transmission or a slipping clutch or other mechanical, electrical, or other problems. If you feel that you cannot handle these issues the best and safest solution is to take the car to a workshop. Get it serviced by an experienced mechanic and sign up for a regular tune-up. These professionals have diagnostic tools such as On-Board Diagnostic (OBD-II) code readers, multimeters, bleeder, and pressure testing kits and vacuum pumps. They also use fuel pressure gauge, circuit testing lights, mechanic’s stethoscope, etc. to diagnose what is ailing your car.