Could a bad harmonic balancer cause a 2009 Honda Odyssey to rev while in park?

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I have a 2009 Honda Odyssey and for the last 2 weeks my check engine light has been on. My engine also sounds like it has a knocking in it. I was recently told that the knocking could be a bad harmonic balancer. Just yesterday I was driving home and as I made a turn my engine shut off. I pulled over and tried to start it back up. I was successful at restarting the engine but then it started revving by itself. It stayed between 2,000-3,000 rpm. I'm not sure what to do. PLEASE HELP!!! When my check engine light first came on 2 weeks ago the codes where cylinders 5 and 6 and random misfire so I changed spark plugs and check engine light is still on. Don't know what else to do.

How long has your 2009 Honda Odyssey had this problem?

About 3 weeks for the engine light and just 2 days for the revving while in park. Also recently put to much oil on and had to get some drained out