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Q: Engine misfiring (?)

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A few weeks ago, i was leaving work and my car started running terribly from start up. just five hours before it had been running just fine. the engine was very hesitant, and felt as though it was very bogged down every time i stepped on the accelerator. throughout the next few weeks, i threw parts at it to no avail. I took it to my mechanic just to diagnosis the issue, and they gave me some parts to try. i replaced the evap purge valve and fuel filter. i got the check engine light read, they told me there was an evap leak (something i'd known about for a while but hadn't gotten around to fixing), and a bad o2 sensor. after replacing one o2 sensor a different one was bad so i replaced that too. it seemed to run a little better, but it's not perfect. if i give it some gas the engine light will flash at high rpms and then stop flashing when i ease off. the engine light doesn't throw a cylinder code.

My car has 126204 miles.
My car has an automatic transmission.

When the engine is misfiring the engine computer may set a code in most instances. If miss only happens at high rpms then this can be cause from a coil that is not able to spark at the higher RPM. The problem is it is hard to know what cylinder or cylinders are misfiring unless a code is set. I would recommend replacing all the spark plugs and test each coil with a spark tester that can test maximum voltage output. If a coil cannot be identified then replace one at a time or replace all of them.

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