It can get frustrating for any driver to expect certain acceleration from their car only to find that the car seems to be hesitant while speeding up. This case could be potentially dangerous in case like entering and exiting the highway from an off-ramp, where retardation may be necessary to be combine with traffic. A car that struggles or hesitates to accelerate may be unpredictable and moments of hesitation may be coupled with equally dangerous moments of surging or unexpected acceleration. When a car is hesitating during acceleration, it should be inspected by a mechanic.

How this system works:

A car with a combustion (gas or diesel) engine requires an exact mixture of fuel and air to run correctly. If this mixture is thrown off in any way, it may cause an engine to run too lean (not enough air), or too rich (not enough fuel). An engine that is hesitate to accelerate is likely dealing with a fuel/air mixture that is too lean. Engine’s that are not running correctly will begin to show signs like hesitation which will only become worse over time. If you notice some signs like hesitation, you should have your car inspected immediately.

Common reasons for this to happen:

  • Mass Airflow Sensor:The mass airflow sensor measures how much air is passing through the engine and relays this information to the car’s computer so that the right amount of fuel can be delivered from the fuel injectors. When a mass airflow sensor faulty, it will typically generate an error code or “Check Engine light.” This warning may be accompanied by hesitation while accelerating, or while driving up in a hill. A vehicle with a failing mass airflow sensor may also stall soon after starting.
  • Fuel Pump:The fuel pump in most modern car sits inside the fuel tank and pumps fuel up to the engine. If a fuel pump cannot provide the right pressure, fuel may have difficulty making it to the engine. A car that hesitates while accelerating or while driving up a hill may have a weak fuel pump.
  • Throttle position sensor:A throttle position sensor tells the car’s computer how far the throttle is open and how hard the accelerator is being pressed. The computer is then able to adjust the fuel/air mixture going to the engine so that is stays at an appropriate level. If the throttle position sensor is not working correctly, it may be sending incorrect information to the car’s computer. The computer may then not provide the engine with the proper amount of air while accelerating, causing a hesitation sensation.
  • Dirty/failing fuel injectors:Fuel injectors spray fuel in a fine mist into the cylinder where it is mixed with air and ignited by a spark plug. Fuel injectors may become grime over time and not be able to provide as much fuel to the cylinder as needed. An unclean fuel injectors may cause the engine to run lean which will in turn, cause hesitation when accelerating.

How it is done:

A mechanic will first plug into your car’s computer using a code reader/scanner to better identify what the exact issue is. In addition to reading trouble codes, he or she should  be able to get readings of oxygen/fuel intake to make sure those numbers are where they are meant be. Once the mechanic gets this information they can begin to fix any potential problems.

If the mechanic believes that the mass airflow sensor has gone bad or is failing, he or she should first examine the sensor for any superficial damage. The mechanic will also ensure that the sensor is wired correctly and that no damage has been done to the wire harness. The mechanic should then remove the mass airflow sensor and change it with a new one if necessary.

If the mechanic believes the problem is the fuel pump, he or she will remove the fuel tank if necessary to inspect the pump. If the pump has indeed stop working, the mechanic will change it. If the fuel tank itself it beginning to show signs of age, it may be convenient to replace the pump and tank at the same time.

If the mechanic suspects the throttle position sensor, he or she will test the throttle position sensor and it’s wiring to see if it is functioning c0rrecly. If it is not, the mechanic will take out  the throttle positioning sensor and the wiring and replace them. In between removing the old sensor and putting the new one, the mechanic should take the opportunity to clean the throttle body. The mechanic will then make sure the new throttle positioning sensor is working properly and transmitting the proper information to the car’s computer.

If the mechanic believe the problem is dirty or failing fuel injectors, he or she will inspect the injectors to check for any signs of damage or leakage. The mechanic should also take this opportunity to change the fuel filter if it is not a part of the fuel pump. They will then change the injectors and test them to make sure they are functioning correctly.

In all situations, the mechanic will start the car to make sure that all of the new components are working correctly. In the event that an issue has caused a warning light to come on, the mechanic will be able to clear the trouble code associated with the light using a reader/scanner.

How vital is this service

Sluggish acceleration can be annoying for drivers who expect more power form their cars, but it can also be dangerous in certain cases. The unpredictable nature of an engine that hesitates can increase the chance of a potential accident especially when trying to combine in and out of heavy traffic. If you notice that your car seems to be underpowered, especially when accelerating, you should not drive it if possible until it can be inspected by a mechanic.