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Discussion Starter · #1 · (Edited)
Hello everyone Im new to forums...just a heads up.

So I have recently purchased a 2018 sti. Two day after the car is stuck at 8.5 psi (Dealer wont help). The car had an after market exhaust (I don't know what type the dealer put a stock one back on) and has a COBB intake. I have tested the boost controller, cleaned the MAP sensor, and checked for any loose or disconnected lines. I'm still stuck at 8.5psi. The only time i can get back to around 17psi (MAX) is after I disconnect the battery. This solution will last for a day or two max. I really don't know what to check next since the car acts fine after disconnecting the battery for a few minutes. I'm not sure if the COBB intake is causing this without a tune or not. Subaru confirmed there is no tune on the car.

PS It does seem to stutter a bit when it is back on stock psi

Thanks in advance.
 

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I'm feeling you're in need of a tune; check your options with COBB depending on what the vehicle has and/or go Open Source.
With the vehicle running "fine" after unplugged you likely are throwing a code or something that the vehicle isn't happy with.
 

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What he ^^^ said. My guess is that the previous owner “unmarried” the Cobb Access Port and kept it. This would have returned the car’s tune to stock. If the exhaust is just an axle back, that shouldn’t be an issue, but the Cobb intake absolutely REQUIRES a retune. The stock tune doesn’t know what to do with all that extra air so it throws a CEL and kicks you down to “limp mode”. A good indicator of this is the cruise control light will start blinking. Again, it’s a best guess, but if I’m right you should be able to fix it by purchasing a Cobb AP and loading the correct tune. IIRC, a new AP3 is about $700 but you can get them used on eBay for less. I would recommend new because then you’ll get full support from Cobb. Tuning w/ the Cobb “off the shelf” tunes is pretty simple and it will set the stage for any future modifications you might be thinking about. Buying the Cobb AP is usually the first mod new owners make to our cars. With hardly any downside and very little risk, even a completely stock WRX or STi will see significant gains by loading a more aggressive tune but with a few core modifications (intake, down pipe/turbo back exhaust) and the correct tune you can make some SERIOUS power gains. Visit the Cobb website, enter your cars specs and you’ll be on your way to a new way of life…good luck. Make sure you post back to this thread if you get it figured out so others may learn from your experience…
 

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Discussion Starter · #4 · (Edited)
Thanks guys that was the issue. Got the COBB AP, and loaded the tune. Now she is running great!

Thank you both for taking the time out of your day to help!

PS: For people looking at this in the future the car did not throw any codes during this. (COBB Intake = Tune)
 
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