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!! RESOLVED!! 2008 Subaru Outback XT Codes P2109 and P0638


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A month ago I put a new engine into this car, and have been driving it gently to break it in. Yesterday I decided it was time to push the pedal a little harder, and after a short burst of acceleration the car dropped to an idle and began to have a rapidly repeating idle surge. I pulled the codes, and it appears there is an issue with the "drive by wire" components, or an idle position sensor. I pulled the codes, have a P2109 and P0638. There are 2 2109 codes and 2 P0638 codes, but they seem to be duplicates. and there is no difference in the information in them other than a timestamp.

Any tips on where I should begin in order to get the issue resolved? Thanks!!

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Edited by ebbsspeed
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8 hours ago, GeneralDisorder said:

Clean the throttle body and if that doesn't resolve it start by replacing the accelerator pedal assembly. They are a known failure item. 

GD

Thanks General Disorder. I'll be out of town for a few days but will clean the throttle body when I return.

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  • 2 weeks later...

Well, I got it fixed. When I bought this car I was told it had a bad knock, and the guy I bought it from had started to take it apart. The intercooler and a few other bits had already been removed and thrown into the back of the car.  I spent about an hour putting it back together to start it. It did have a knock that was the worst I'd heard, outside of a diesel dozer starting in cold weather. Long story short, I put a brand new short block and rebuilt heads in it, and had been driving it gently for a bit to break it in. When I finally did put my foot into it, the stuff I mentioned in the original post happened.

Based on lots of internet looking and some of the suggestions in this thread, I decided I'd try a new accelerator pedal assembly. I had the same issue afterwards, so started to pull parts to get at the throttle body. When I got the rubber boot between the intercooler and the throttle body pulled loose, I noticed the butterfly was partially open. I doused it with cleaner to see if that would free things up, but it looked fairly clean before I sprayed it. I pushed on the butterfly a bit and a "thing" that was jammed between the butterfly and body fell out, and the butterfly closed. I consider myself quite lucky that the "thing" which got blown into the throttle body when I put my foot into it never made it past the butterfly to an intake valve. I don't know if I somehow dropped this "thing" into the intercooler, or if it was dropped in there when the previous owner threw parts into the back of the car. I typically bag and label things as I disassemble something I am not familiar with, and this was my first experience with a DOHC turbo Subaru, so I was extra cautious in bagging and labelling everything I removed. 

Cleared the codes, did an idle relearn procedure, and all is well.

The "thing" was a stainless steel lock washer. 

 

Subaru Washer.jpg

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  • ebbsspeed changed the title to !! RESOLVED!! 2008 Subaru Outback XT Codes P2109 and P0638

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