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Need help diagnosing possible engine problem.

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I have a 2006 Legacy GT SpecB with COBB downpipe and full exhaust with COBB Stage 2 tune from Accessport V2.


Lately I have noticed that when I accelerate around 2-3000 rpm the car stutters but continues to accelerate, vibrating the car, and lacks in power throughout power band.


So far, we have searched for vacuum leaks from the top of the engine bay and did not find anything. As well as checked air filter and mass airflow sensor. We also plugged in the Accessport and went for a drive, monitoring boost, and would peak at 9.6 pounds of boost. All fluids seem to be normal so I am trying to get some feedback as to what my problem may be before I take it in and spend a bunch of money for someone to figure it out.


Thanks for the help!

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Any misfires detected - and any knock detected?


Also make sure you don't have any loose heat shields or similar stuff since they might cause the knock sensor to go in. A wastegate not closing correctly can also be a factor.


More pieces that may play a factor is the MAP and O2 sensor in addition to the MAF.

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Have you cleaned the MAF lately ? It's a once a year thing.


How are the engine grounds ?


O2's will normally throw a CEL.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.


Engine Build - Click Here

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