In a pedal follower system, the ECM controls the throttle plate position to match APP sensor input. The APP sensor 'commands' the throttle. In a pedal commander setup, the ECM opens the throttle based on other data like engine load and RPM, with the APP sensor providing more of a 'suggestion'. This allows for smoother operation and more consistent idle. Consulting the service manual can confirm which type a particular vehicle uses. Regardless of setup, a correlation issue between the APP and TP sensors can trigger P2135.