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Discussion Starter · #1 ·
I've got a 2005 outback xt that will go into limp mode every month or two while throwing a P0638.

Symptoms:
-Idle hunting, rpms jump up and down
-intermittant high rpm at low speeds/idle while off gas pedal
- Limp mode about once a month

With an obd 2 reader the throttle position moves up and down with the idle hunting.

I have:
-cleaned replaced the throttle body, which fixed high idle
-reseated the pedal connector
-fixed leaky intercooler
-unplugged o2 sensors

So far same idle hunting and occasional dump to limp mode. I have a new ECU coming in the mail.

There is also oil in the throttle body and turbo outlet. I believe oil is coming from both the turbo and the other side of the throttle body.

Any help or insight greatly appreciated!!
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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The electronic throttle has its own relay. It's behind the glove box. Since the issue is sporadic and intermittent, I would suspect the relay or a problem in the harness to the throttle motor. There is some electrical diagnostics necessary to verify. I'd have to post the diag steps after I get to the shop, (copy and paste). You need a test light and multimeter along with the tools to remove the glove box.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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16,149 Posts
First pic is the relay location behind the glovebox. The rest is the diagnostic procedure to determine the issue source with pinout and wiring diagram.
 

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Discussion Starter · #4 ·
First pic is the relay location behind the glovebox. The rest is the diagnostic procedure to determine the issue source with pinout and wiring diagram.
Thanks a ton, I'll give it a shot and report back.
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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The majority of fixes for this (even on the LGT forums) is to replace the throttle body. Oil intrusion past the throttle blade shaft can cause issues to the position sensors.

While pretty common to have a throttle body fail, age, oil, or previous abuse (working the blade by hand) can cause issues.
 

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Discussion Starter · #6 ·
I've already replaced the throttle body, it says in the original post. Thanks though!
 

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Im having a similar issue, but assuming its due to the -40*F weather we are having in Whitehorse, Yukon. P0638 error, car in limp mode, constant CEL with flashing cruise. I have an "arctic" package on the car (battery, block, oil heater) but didnt leave it plugged in when I flew away for a weekend. Car barely made it home. Car seems to idle FINE, just in drive won't exceed 15 mph. Wondering if I should replace the TB (2+ weeks for shipping) or just find a garage to thaw her out in...
 

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2008 Subaru Tribeca
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930 Posts
I recently had a 09 outback 2.5i same issue, hard fault for the code.
Replaced ecm and that fixed my issue.
 

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Discussion Starter · #9 ·
I replaced the relay that was mentioned but still no luck, the rpms wiggle around at idle. I'm going to throw in the ECU and see if that fixes it, I'll write back once I know.
 

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Discussion Starter · #10 ·
Im having a similar issue, but assuming its due to the -40*F weather we are having in Whitehorse, Yukon. P0638 error, car in limp mode, constant CEL with flashing cruise. I have an "arctic" package on the car (battery, block, oil heater) but didnt leave it plugged in when I flew away for a weekend. Car barely made it home. Car seems to idle FINE, just in drive won't exceed 15 mph. Wondering if I should replace the TB (2+ weeks for shipping) or just find a garage to thaw her out in...
I would say thaw the thing first, I wasted 150 in parts replacing mine and it didn't fix anything
 

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Discussion Starter · #11 · (Edited)
ECU did it. Be aware the XT model has an immobilizer that's a wireless chip in the key. You gotta get the key reprogrammed to the new ECU so it starts, otherwise, it will just turn the starter indefinitely. I got a local locksmith to do it for like 20$ with his fancy computer thingy. Get a used one dont bother the 600$ for new one.
 
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