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Is the misfire gone? As far as the power loss, the first thing that comes to mind is a plugged catalytic converter. If the misfire was allowing raw fuel to enter the exhaust, it could have damaged the converter.
What kind of noise are you hearing? Has the check engine light come back on? Was the only code saved when the original problem started a P0303?
Can you describe the noise to me? If possible, can you record the sound and upload it for me to hear?
Here is a link that explains symptoms of a bad catalytic converter. The second link explains how to test one. It shows the converter being disconnected from the system. However, if you remove the upstream oxygen sensor (before the converter) it can help. It won't run perfect, but if there is a restriction, you should notice a difference.
https://www.2carpros.com/articles/bad-catalytic-converter-symptoms
Here is the test:
https://www.2carpros.com/articles/how-to-test-a-catalytic-converter
Let me know what you find.
Joe
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Friday, August 2nd, 2019 AT 8:54 PM