From what I learned on here the front O2 sensor is the one that mess's with the fuel mixture.
You may want to replace that one first.
Then clean the MAF sensor with the cleaner for it, then think about getting the car tuned and off the OEM map.
Check out Mike's "m sprank" site, www.infamousperformance.net
He can guide you on what you should do.
203,000miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. CHECK your oil, these cars use it.
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