I am a shade tree mechanic with no formal training (other than years of trial and error). I am by no means an expert or a professional. Any insight is greatly appreciated.
I recently purchased a Base 2012 Countryman for my son. It has recently started generating a P2138 Code, which indicates an issue with the accelerator position sensor. I replaced the APP, erased the code, and it was fine for my test drive. I tried to restart it after a few hours, the check engine light came on, and the car had the same symptoms: sluggish acceleration. I turned off the car, waited a few seconds, and restarted. The issue was gone. I tried again a bit later, and the check engine light came on again. I shut down for a few seconds and restarted, and the issue was gone again. It seems to be ok now, and I haven't run a scan again to see what DTCs are present. Is there a relearning procedure, or does the ECU take time to relearn while driving? I wnr through and made sure the harness was plugged into the accelerator pedal assembly. I will go through and check the harness for any physical defects. If I am checking the actual sensor pins/wires (11,12,13,14 not the 5v reference), what signal/voltage am I looking for?

 

See the graph on page 46 of the attached PDF. One signal should get close to 2 VDC, while the other close to 4 VDC at full throttle, regarding #11 & #12 of your image.