Skip the auto shop - Our mechanics make house calls

Q: Engine is very strong on hard acceleration, but on light acceleration it misfires, also rough idle and smells way too rich.

asked by on

When driving around 40 mph, everything seems normal and smooth. Wide open throttle burst will pin everybody back in their seats! But light acceleration will produce misfires (bumpy feeling).

Engine is pure stock except for dual electrode spark plugs. New cam belt. New battery. Transmission is the original 4 speed automatic. New fuel pump module about two years ago. All gauges indicate normal operation, including temperature. All original except for starter, power steering pump, power steering rack, timing belt, water pump and internal belt tensioner. All brake stuff has been replaced as needed.

My car has 248000 miles.
My car has an automatic transmission.

This may be related to a faulty throttle position sensor or potentially a dirty or failing mass air flow sensor. The mass air flow sensor is a unit in the intake system that monitors air intake as it is mixed with fuel prior to being injected into the motor. When this is dirty or faulty, this causes an imbalanced air/fuel load to be supplied to the motor which results in an over fueling or under fueling situation depending on the conditions. This type of inconsistent fuel supply to the motor may cause a hesitation, loss of power, a jerking reaction, potentially a bit of black exhaust smoke and typically a strong smell of fuel when this sensor is malfunctioning. When this is not working properly, you may also notice a strong smell of fuel. I would suggest having a professional from Your Mechanic come to your home to diagnose your mass air flow sensor.

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
  • Engine is very strong on hard acceleration, but on light acceleration it misfires, also rough idle and smells way too rich.

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: Problem with the dash and gauges when driving on a bumpy road

This can often times happen when the ABS system is activated which is usually activated when driving over rough surfaces or bumps. The ABS system will trigger warning lights and typically cause a momentary lapse in traction control as the...

Q: Timing is good, fuel system is good, the car has spark, distributer is dead center and starter is good. Battery is brand new but c

Hi Brunie. It's possible that your EGR valve is damaged or clogged with a tremendous amount of carbon debris. If the vehicle has been sitting for a while, it's possible the gasoline is bad. To be completely honest, without knowing...

Q: Should my car not be driven out of town if all the above is happening?

The Check Engine Light may be caused by many different things. The shaking may be caused by a poor fuel delivery problem such as a faulty or dirty mass airflow sensor. The mass air flow sensor reads air intake as...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...