You would hear a boost leak if it was at the connector where it clamps on the tmic to TB.
IMO a bad O2 will not cause a misfire.
If it was to rich, car should run like crap.
You may need to pull the spark plugs, how long have they been in there ? they should be replaced every 60,000 miles.
178,000+ miles, 5/20/12 new ej257 short block, 8/20/11 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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