Subaru Outback - Check Engine P0506

A couple of weeks ago I was driving my car and the check engine light came on. Within a minute of the light coming on I lost the ability to accelerate. I pulled over and returned home. I have a CAN ODB2 code reader that I hooked up the car to and pulled 1 code with the number of P2138. I looked up the code and its description is “Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation.” Doing a bit more looking around it sounds like this is a common problem with Subaru Outbacks (source website). The problem was an intermittent issue with the “check engine” light going off sometimes and coming on at others. Always with the same code however. Turns out that the best fix for this is to replace the accelerator pedal assembly, so I ordered the part and swapped it out. I drove the car around for a few days and the issue went away and I did not get the check engine light anymore.

However, I know that although sometimes the check engine light is not showing, sometimes the codes are left behind in the computer. So I hooked up the CAN ODB2 reader again and sure enough the code was still present so I went through and erased the code. Before fully erasing the codes however, the reader mentions that it can also remove other items in memory. But I went through and cleared it still. However, as soon as I started the vehicle, it sounded like it was about to stall out. Almost the way a stick shift sounds when you are in a really high gear or you don’t clutch it fast enough and it turns off. Initially, it would only do that when I started the car or when I stopped at a red light but the vehicle would not “stall-out”. Within a day after clearing the codes the “check engine” light came back but now the code is P0506 with a description of “Idle Speed Control System (ISC) RPM lower than expected”. As of today the car is actually stalling out sometimes when I start it and other times when I am at a stop light. Essentially anytime the RPMS go down close to 0.

There’s tons of information out there about it being a problem with the air control valve, throttle body, a faulty PVC etc. But this problem did not start until I cleared the memory in the car. I had read a while back that doing that can cause the engine control computer to ‘forget’ the existing parameters for idle speed and such and that putting a few miles on the vehicle will correct the low idle as that allows the engine control computer to bring the operating parameters up to date again. I had reset codes on the car a few years back and I recall that the auto shifting took a bit to relearn when to switch gears but I never had stall-out problems.

Any assistance you can provide would be appreciated.

Vehicle: Subaru Outback 2006

Rather than “internet diagnosing” the problem by endlessly discussing it… Go out and clean your throttle body. Clear the code and test it.

Post back with the results and we’ll go from there… if we need to.

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Thank-you for your suggestion. However, based on the information that I had provided someone else suggested doing an idle relearn procedure and it fixed the problem.


Glad you got your car working well again. The symptoms did seem like the idle parameters got erased somehow. Those parameters probably revert to what they were when car was new, but gunk has accumlated in the engine over time and affecting both air-flow and fuel-flow, so some adjustments to the idle parameters has to be made. Fortunately the manufacturer provided an automatic way for the drive-train computer to do determine what changes to the idle parameters are required.

Glad that it’s fixed, and you did the right thing by seeking advice.
The various Subaru model specific fora often are good information sources, too.

As a general rule, when one of our cars throws a code the first thing I do is disconnect, clean, and reconnect the contacts of any involved sensors. treating them with a suitable contact protector prior to reassembly - this has cleared many of my problems. If the part is serviceable or needs cleaning, such as a throttle body, that should should be done. Only then would I try replacing an expensive part (unless an initial inspection showed it obviously had failed).

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That’s good advice. Thank-you Ken, I ill keep this in mind for next time.