Cylinders misfiring code p0304 and p0300?

Best thing to do now that its running smoothly the actual codes might be old id erase them at this point and wait to see if they come back they might not after youve done the work thats said "
Heres a few Things to check that can cuase or at least contribute to a mutible random misfire you might have already checked some of these .. first and formost the coil for 1 and 4 where your getting the misfires is a single coil running both cylinders 1 and 4 on this vehicle you said its been replaced but It might be defective if it keeps misfiring depending on where you purchased it and check the ground and all other wires and plugs leading to the coil..and also ..is there any chance you might have damaged the reluctor ring mounted to the back of the harmonic balancer vary important if a tooth is evan slightly bent or damaged in any way it can cuase this especially at high rpm but not so bad at lower rpm ..and or damage to the crank sensor plug and wires down there while working with the hamonic balancer ..check these too
Maf.. map.. cam.. crank.. knock.. coolant sensors .egr ..evap ..Vacuum hoses wherever you see them
Dirty throttle body and tps sensor..
Plugs leading to sensors wherever you see them
Grounds everywhere you see them engine firewall fender wells various places around the vehicle
Check and clean the plugs for injectors at cyl 1 and 4 if the problem persist
Look at live data with your scan tool short term fiel trim you might see abnormalities
Check the bolts in the intake manifold somtimes they can be loose close to the area of the suspected cylinder can leak there torque them if nessary
Fat hose to the brake booster leaky ? Also good luck hope this helps for what its worth

Thanks for the quick feedback. I'll touch base with the mechanic that did the haarmonic balancer install.

Best thing is you say the check engine light is coming on but goes back out so like i said id earase the codes reset the ecu and wait to see if they return if any at all they.might not ..good luck hope this helps

Ok but keep in mind its most likely the coil in this case with this vehicle is ash him where he got the coil from theres been alot of problems woth weak coils lately they migh funtion well ant lower rpm but can keep up at the higher rpm wich sounds like problem youre having best of luck let os know how it turns out

The error codes were new. They reappeared after I had replace the spark plug wires and ignition coils. I purchased them at Autozone.

The mechanic did the harmonic balancer, AC compressor and serpentine belt.

That figures id take them back or at least the bad one for cylinder 1 and 4 and trade it in for another one most likely its was defective theres been problems in this category woth weak coils that cuase this exact problem there a good chance its the coil...be well" good luck

Unless you have one of the old ones that is known to be good you could just switch it out to see if the problem solves that way too just food for thought good luck

Thank you.

No worries glad to help

Problem resolved after much troubleshooting. Thought you would like to know what rectified the issue. The mechanic ran a bunch of tests then decided that a computer reset might be needed. He did the reset procedure and the misfires vanished. Somehow replacing the harmonic balancer triggered the issue but resetting the computer rectified it.

Yep" its usually a pretty good idea to go back to the last mechanic that worked on it while its still fresh in theyre mind becuase when the cars right in front of them they can see alot more and somtimes helps them figure it out pretty quickly also helps when the car is put into and environment that has all the diagnostic tools availible to really measure things and get to the bottom of it fast...well thats great news glad to hear you have your car back and remember we're always hear to help ..thanks