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Old 09-13-2017, 01:45 PM   #1
cowboydandy
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Member#: 474459
Join Date: Sep 2017
Chapter/Region: SCIC
Location: Sunland, CA
Vehicle:
2011 Impreza WRX STI
Plasma Blue Pearl

Default Car pulling p0420 and p0171 codes

I own a 2003 WRX with 201,000 miles. Recently put a new motor in.
Modifications include; catless downpipe, catless midpipe, and Borla Hush catback.
The car recently started to idle very weird and every time I would creep up at a street light I would rev up to 1300 rpm's and come off the throttle the revs would drop below 900 and come back up. I checked my intake and there was a slight gap where it connected to the turbo inlet hose. I closed that up and as soon as i did the car started to idle even worse. The car sounded like the revs were going up and down. My boost gauge was showing that. So i ended up taking my stock airbox and replaced it with a short ram intake that I own. The car started revving fine and drove much better but now I the car has a p0171 code 01/02. The car runs fine but everytime i cold start it the car dies immediately unless I give it a few revs.
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Old 09-13-2017, 02:39 PM   #2
Charlie-III
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Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
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1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

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OK, I'm a NA guy but reading up on turbo Subaru due to my sons car.

Do you have a tune? If so, what?
Even COB has no OTS map for a CATless DP. Get a protune or email tune.

2003, I believe you still have a cable for gas, check your IAC.

When was last tuneup?
Any CEL's?
After repairs, did you clear the ECU?
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Old 09-13-2017, 04:22 PM   #3
cowboydandy
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Plasma Blue Pearl

Default

Quote:
Originally Posted by Charlie-III View Post
OK, I'm a NA guy but reading up on turbo Subaru due to my sons car.



Do you have a tune? If so, what?

Even COB has no OTS map for a CATless DP. Get a protune or email tune.



2003, I believe you still have a cable for gas, check your IAC.



When was last tuneup?

Any CEL's?

After repairs, did you clear the ECU?


Okay so I don't have a tune and I know I need a tune for every little thing I do to this car but the turbo back hasnt caused problems since installation.

The IAC valve?


Last tune up was 3000 miles ago. That was oil, spark plugs, and fuel filter.

Forgot to reset ecu after repairs. I'll try that now. Thanks!
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Old 09-13-2017, 04:46 PM   #4
cowboydandy
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Member#: 474459
Join Date: Sep 2017
Chapter/Region: SCIC
Location: Sunland, CA
Vehicle:
2011 Impreza WRX STI
Plasma Blue Pearl

Default Car pulling p0420 and p0171 codes

And I have two CEL'S right now. 2 p0171 and 2 p0420.

Edit: grammar.

Last edited by cowboydandy; 09-13-2017 at 04:54 PM.
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Old 09-14-2017, 10:00 AM   #5
Charlie-III
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Silver Sleeper BK, 5MT

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IAC = Idle Air Control.....it bypasses air around the throttle plate to maintain idle speed on cable driven throttle bodies.
On DBW engines (drive by wire) the ECU controls the throttle plate, no IAC.

As to CATless exhaust, there is a whole host of potential issues running either stock tune, or a tune not set up for CATless. As I mentioned, I don't believe ANY tuner has an OTS map for CATless, they all recommend a special tune.
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Old 09-14-2017, 11:01 AM   #6
Samurai Jack
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What's different about the new motor from the old motor?
- Is it stock?
- Is it "built"?
- Is it an EJ205?

With a 2003 OEM motor, you can run catless UP & DP with no real issues.

Sounds like your problem is air related:
- Dirty IACV
- Dirty MAF
- Vacuum leak(s)
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Old 09-14-2017, 12:12 PM   #7
MadScientist84
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WRB

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i know this sounds like redundant, but clean you MAF
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Old 09-14-2017, 12:18 PM   #8
cowboydandy
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2011 Impreza WRX STI
Plasma Blue Pearl

Default

Quote:
Originally Posted by Charlie-III View Post
IAC = Idle Air Control.....it bypasses air around the throttle plate to maintain idle speed on cable driven throttle bodies.
On DBW engines (drive by wire) the ECU controls the throttle plate, no IAC.

As to CATless exhaust, there is a whole host of potential issues running either stock tune, or a tune not set up for CATless. As I mentioned, I don't believe ANY tuner has an OTS map for CATless, they all recommend a special tune.
Okay, I will check the IAC and clean it. Hopefully that helps my issue. Thank you.
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Old 09-14-2017, 12:21 PM   #9
cowboydandy
Scooby Newbie
 
Member#: 474459
Join Date: Sep 2017
Chapter/Region: SCIC
Location: Sunland, CA
Vehicle:
2011 Impreza WRX STI
Plasma Blue Pearl

Default

Quote:
Originally Posted by Samurai Jack View Post
What's different about the new motor from the old motor?
- Is it stock?
- Is it "built"?
- Is it an EJ205?

With a 2003 OEM motor, you can run catless UP & DP with no real issues.

Sounds like your problem is air related:
- Dirty IACV
- Dirty MAF
- Vacuum leak(s)
The new motor is a a 2003 wrx oem motor. I have been running the UP and DP fine. I took the short ram off this morning because i assume I would need a tune to run that.

I haven't checked the IACV so I will today.. MAF sensor was thoroughly cleaned.
Thank you.
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