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2005 Scion tC still shows CEL after new coil

My car was shaking while in drive while stopped. My check engine light went from flashing to staying on back to flashing. I was receiving a cylinder 3 misfire code after I changed oil and all spark plugs. I just changed the coil today and the check engine light is still on. Why??

Because there is still a problem!

Read out the codes it is setting now and post them here and we will try and help. The P1234 code, not just the description. Oh, and don’t drive it while the CEL is flashing, damage can occur!

P0303 is the code. It said to change the coil, which I have done. I also changed the spark plugs and gasket cover valve, which was causing the original oil leak. I also changed the oil and spark plugs because they were drenched in oil. After that is when I changed the coil. The vehicle is no longer shaking but the check engine light is on still reading cylinder 3 misfire. And code is telling me change coil

A P0303 code is telling you what is wrong, not what to do about it. A misfire on #3 could be a bad coil, sure, bad plug, bad wire, faulty wire connections TO the coil. It could also be a bad injector for #3 or even a defective engine computer. And it could be that that cylinder has a bigger problem like a burned valve or low compression.

Now you tell me this. Plugs drenched in oil (if you mean the electrode was oily wet) tells me the rings are worn out. #3 is worn more than the others so it misfires badly enough to throw a P0303. I’d suggest you run a dry and wet compression test on the engine as I suspect there is a serious problem in #3. Low dry and wet compression points to a burnt valve. Low dry and OK wet compression tells me the rings are at fault. Good Luck.