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My 2005 Outback has about 148,000 miles and is AT.

The P0638 only occurs after about an hour of highway driving. Symptoms are immediate loss of power. The car becomes can barely move itself and idle is rough. I then Turn the car Off and wait 30 seconds. When I start the car it will drive normally for 5-10 minutes before it happens again. If you drive it very moderately at 40mph it seems to not happen as frequently. Working it hard seems to bring it on more rapidly.

I have read a common cause of this fault is a bad accelerator pedal. So I replaced that with no cure. Another possible cause is a bad Throttle Position Sensor, which is fully integrated into the throttle body. So I replaced the throttle body and it's GPS with a used throttle body. The replacement was faulty and the problem got much much worse. So I got a new Throttle Body and GPS for $125. Still no cure, and it went back to being a problem only occuring after about an hour of highway driving.

Seems like another cause could be the ECM? Any suggestions?

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