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 December 08, 2016

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.

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