What sort of codes do you pull up?
You mentioned EJ20Y swap, which ECU are you running?
Legacy/Outback owners have reported this, I'm dealing with something similar in my EJ20Y swapped 06 Legacy.
See if this thread helps: https://legacygt.com/forums/showthread.php/p2138-throttle-pedal-position-sensor-switch-150344p8.html?highlight=P2138