Q: Cylinder 4 misfire code P0304

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A few weeks ago my check engine light came on solid and noticed my car was idling rough and very sluggish from a dead stop up to 30mph. I had it checked out by the guy who has worked on my car for years and is usually pretty on point because he actually worked at Hyundai in Korea. After running the codes it was determined that it was a P0304 misfire. He changed the plugs, wires, coil pack, injector, and blew it out and I still continue to have the same performance issues with the light still on and blinking at times. My mechanic is puzzled. Help please!

My car has 110000 miles.
My car has an automatic transmission.

You should recheck computer to see if same code is coming up P0304? If it is then check plug wire to see if it has oil on it from a leaking valve cover gasket getting oil on plug wire and plug shorting it out. If all plug wires are dry then you will need to have a compression test to see ig cylinder has low compression? Also check to see if any intake vacuum leaks.

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