My car hesitates and I have to press on gas hard for it t...

Q: My car hesitates and I have to press on gas hard for it to kind of smooth on out.

asked by on December 07, 2016

Well when taking off my car hesitates, make rumble noises and shakes a little bit
My car has an automatic transmission.

Typically, what you are describing is due to an engine management fault(s) and such faults occur in ignition system components, the fuel system, and/or the air induction system. A possible first approach is to just simply make sure that the spark plugs are not past due for replacement and that all other engine maintenance is up to date. If the problems remains unresolved, one would request a diagnostic for poor or rough acceleration.

There are quite a few items to consider during such a diagnostic, but here a few major items:

Mass Airflow Sensor: The mass airflow sensor measures how much air is entering the engine and relays this information to the vehicle’s computer so that the right amount of fuel can be delivered from the fuel injectors. When a mass airflow sensor begins to fail, it will typically generate an error code or “Check Engine light.” This warning may be accompanied by hesitation while accelerating, or while driving up a hill. A vehicle with a failing mass airflow sensor may also stall soon after starting.

Fuel Pump: The fuel pump in most modern vehicles sits inside the fuel tank and pumps fuel up to the engine. If a fuel pump cannot provide the correct pressure, fuel may have difficulty making it to the engine. A vehicle 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 vehicle’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 properly, it may be sending incorrect information to the vehicle’s computer. The computer may then not provide the engine with the correct 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 dirty over time and not be able to provide as much fuel to the cylinder as is needed. Dirty fuel injectors may cause the engine to run lean which will in turn, cause hesitation when accelerating.

To resolve the issue, please request a diagnostic for poor or rough acceleration. If you have additional concerns or questions, don’t hesitate to re-contact YourMechanic.

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