Q: Engine is misfiring on my car

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The engine is running roughly on my car. It seems like the engine is misfiring; it bucks and vibrates. I did a tune-up (replaced spark plugs and coils, and air filter), put in fuel cleaner, and removed the idle air control valve to make sure it wasn't stuck. None of that helped. Could it be the mass airflow sensor? Someone had suggested to me that I should unplug the sensor and start the car to fix the problem, but that didn't work. Any ideas?

A faulty mass air sensor can cause rough running due to the injection mapping being improperly set. Unplugging the sensor can, in some cases, cause the rough running to clear up as a fault is set and the engine computer runs the vehicle off of preprogrammed values.

Since this did not help, the first thing to look at is the possibility of an unmetered air leak or vacuum leak. A smoke test of the induction system is a quick and easy way to locate an induction system leak. You may also want to have fault codes cleared and then read out after a drive cycle to see what comes back. A faulty oxygen sensor for example, can also cause rough running issues. You may want to enlist the help of a mechanic who will have the diagnostic equipment and training necessary to correct this rough running condition.

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