Skip the auto shop - Our mechanics make house calls

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

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  • Home
  • Questions
  • My car hesitates and I have to press on gas hard for it to kind of smooth on out.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: The AC starts out cold but doesn't stay cold, blows out cool air after about 20min.

Hi there. Sometimes a compressor clutch failure or restriction from the low pressure side of the AC system can cause this type of problem. In other cases, it'll be due to a refrigerant leak. It's always a good idea to...

Q: Car shaking, grating noise in reverse

Hello. If there is no grease on the axle, this may cause the car to shake and make grating sounds while driving. This happens because the grease that is in the axle lubricates the other moving parts in the axle....

Q: When started it struggles to idle and cannot even rev.

Hello. This can be caused by a few different things. It can be a sensor problem, an internal engine issue, or just need a tune up. I usually start by scanning the computer for any codes. If there are codes,...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.