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Q: Check engine light on, error code P0300, P0302, P0171,

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Check engine light is on, steady most of the time, but sometimes, the check engine light flashed for a short while then turned steady again after I slow down. If I drive only 30 miles/hr or under, check engine light remained steady, no flashing.

All 4 spark plugs and ignition coil #2 were replaced today, it did not help. Should I still drive the car at about 30 miles/hr until a friend helped to change the up stream oxygen sensor free. It would take another month before this friend has time. Thank you !

My car has 124500 miles.
My car has an automatic transmission.

Hi there. Why are you going to replace the O2 sensor? Did testing reveal a problem with the sensor itself? It sounds like there could be an air leak concern or an airflow meter concern. Has anyone checked for cracked, leaking, or loose vacuum hoses? Has the airflow meter been tested against specifications? Pull the airflow meter out and check the self cleaning wire element to see if one side is covered and not clean, if not then replace the meter and recheck operation; inaccurate airflow readings can create misfires. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several technicians available that can assist you with a check engine light inspection.

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