Car Not Accelerating Like It Used To

Foot on vehicle accelerator pedal

When you step on the gas pedal, you expect your car to respond by picking up speed based on how hard you press down on the pedal. Vehicles that are receiving ample fuel and are otherwise well-tuned, should take off as expected. When this action doesn’t occur, and instead the car hesitates or accelerates slowly, the car may be experiencing trouble with the fuel or emissions system. A car that has trouble accelerating should be repaired immediately as you may be placing yourself in harm’s way, especially when attempting to go up a hill, merging onto the freeway, or at intersections.

Combustion engines are designed to have fuel delivered to the engine and dispel exhaust gases away from the vehicle. Many components and sensors work together in order to accomplish the combustion process and propel your vehicle forward. When there is a failure within this system, the car may experience acceleration problems. More often, these issues occur from a failure somewhere in the fuel system.

Reasons your car is not accelerating like it used to:

Mass Air Flow Sensor (MAF) Dirty or Faulty

Located and attached to the inlet air cleaner, this sensor measures the air flowing into the engine air intake system. A dirty or faulty MAF could be sending the incorrect data to the car’s internal computer when calculating the air to fuel mixture.

Oxygen Sensor Malfunction

The oxygen sensor monitors the oxygen emissions of the vehicle to help analyze the air-fuel ratio going through the engine and sends the information to the car’s computer. If the sensor is damaged or has malfunctioned, the engine is unable to regulate the air-fuel mixture which will result in the engine running rich or lean and slow acceleration.

Throttle Position (TPS) Sensor Malfunction

Controlled by the accelerator, the TPS detects the angle of the throttle valve opening and sends the data to the computer. The engine speeds cannot be controlled by the accelerator if the TPS malfunctions and may cause the engine speed to increase or decrease unintentionally.

Clogged or Dirty Air Filter

Air filters are designed to catch debris and other impurities from air provided to the engine for the combustion process. If an air filter is clogged, the engine will not have enough air to create the correct ratio of air and fuel resulting in slow acceleration.

Timing Belt

Linked to the camshaft and the crankshaft, the timing belt helps to manage the pistons of the engine. The camshaft controls the opening and closing of the valves while the timing belt controls the timing of this process. If the timing belt’s alignment is off, even by just a smidgeon, it can cause acceleration problems.

Failed Catalytic Converter

Catalytic converters ensure the proper amount of exhaust exits the engine. When the “cat” fails, an improper amount of back pressure is created, changing the engine’s ability to flow properly. In addition to acceleration trouble, the engine will not feel as powerful and run hotter than usual.

Fuel System Troubles

Since the engine needs fuel as part of the combustion process, when fuel is absent or is present in only very small amounts, the engine will have difficulty with acceleration. The fuel delivery process may starve the engine of fuel as a result of a:

  • Clogged or dirty fuel filter – A dirty filter, clogged with debris and other impurities will hinder the engine’s ability to receive the proper amount of fuel.
  • Faulty/Clogged fuel injector – Fuel injectors control the amount of fuel that is released into the combustion chamber and have tiny passages to deliver fuel. Over time, the passages become clogged from contaminants in fuel making fuel delivery very difficult.
  • Defective Fuel Pump – Fuel pumps pull fuel from the gas tank to the engine via the fuel lines. If the fuel pump gives out or becomes clogged, it will be unable to supply fuel to the injectors and may result in poor acceleration, sputtering, or stall outs.

A car that will not accelerate properly or hesitates should be inspected and repaired immediately. Continuing to drive with this sort of trouble can be rather dangerous. Even if the trouble is as simple as replacing an air filter, it’s better to err on the side of caution than risk your safety. Seek out a trusted, professional technician to fully inspect your vehicle and determine what is causing your vehicle’s acceleration problems to have it repaired properly.