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!
  1. Home
  2. Questions
  3. 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: No start issue

These lights are all designed to come on when the key is in the on position prior to starting the vehicle as the computer goes through a series of system checks making sure that each of those systems is working...

Q: I have a 1988 dodge dynasty. The timing jumped and I've been told the engine is not longer good. The car cranks but doesn't start

Hi there. I think this is an example of somebody telling you something that does not comprehend the basics of ignition timing or the timing chain / belt. Ignition timing is a collaboration between the ignition system and the valves...

Q: My Jaguar XJ8 is running extremely rough

Being that your car is running better with the MAF disconnected, I say replace your MAF. Most cars would shut off without the MAF connected. If you need a technician to scope out the problem in person, a certified professional...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...