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Old 11-13-2018, 05:12 PM   #630
Scooby Newbie
Member#: 430276
Join Date: Sep 2015
Chapter/Region: South East
Location: Melbourne, FL
2007 Stage 2 STI
Obsidian Black Pearl


I guess I'll add to the list to see if anyone else can help.
I am having a P0171 code on my 07 STI as well...
This code popped up after the following 3 things happened:
  1. Took car to Subaru to get fluids flushed (diff/trans/power steering/brake)
  2. Ran Wawa 93 Octane gas for the first time (I had a gift card...)
  3. Installed GD STI 08+ Steering Wheel and SWC
Relatable Mods:
  • Cobb SF Air Intake
  • Cobb Turbo-back exhaust
  • Tomei UEL Headers + Uppipe cerakote (black ceramic coated)
  • IAG Black TGV Deletes
  • Perrin silicon turbo inlet
  • Street-tuned by Mikey Botti November 2017
  • Koyo Radiator w/ Mishimoto 2 big radiator hoses
  • Crawford AOS
  • Walbro 255lph Fuel Pump
  • Grimmspeed lightweight crank pulley
Things I have tried:
  • Replaced front O2 sensor (it was replaced a few months back diagnosing a p0172-rich, but that turned out to be dirty MAF)
  • Tested MAF with someone who removed theirs (speed density), no change
  • Replaced MAF with denso, no change
  • Replaced stock fuel pump with Walbro 255
  • Replaced fuel pressure regulator
  • Replaced fuel in-tank filter
  • Replaced MAP sensor with a working one, no change
  • Replaced coolant temp sensor with a working one, no change
  • Cleaned fuel sock
  • Ran fuel system/injector cleaner in tank
  • Boost/Vac leak tested twice (once with 15psi pressurized, once with a smoke test machine) no issues
  • No noticeable exhaust leaks (had car up on lift couldn't hear or feel anything)
  • Compression/leakdown test, no issues
  • Checked ground connection on driver side of intake mani-no issue
  • Swapped injectors/coils/plugs around (since Cyl 4 was having big misfires) and misfires did not follow
  • CEL P0171
  • 25% fuel corr. at idle
  • AFR up near 17/18 at idle
  • AP Boost Gauge near 10psi at idle
  • Roughness/Misfire on Cyl 4 random at idle (sometimes up to 20 counts)
  • Random small Roughness/misfire counts on other Cylinders (1-2 counts)
  • Car canít reach peak boost anymore (20psi, only getting 17psi)
  • Car runs a little richer (AFR gets closer to 14.7) at idle when AC is ON (when AC cycles it gets closer to 14.7 then drops back up to 17-18)
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Last edited by Gumdrop; 11-17-2018 at 08:08 AM.
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