Theory Of Operation
WARNING: This page is about a different car, the 2024 Jeep Grand Cherokee L. However, it is still accessible from the selected car via links, so may be relevant.
The objective of the "Idle Speed Rationality" is to monitor the ability of the Powertrain Control Module (PCM) to achieve and maintain a steady idle condition. The Engine Speed Error is calculated by comparing the actual engine speed to a target idle speed. If the actual engine speed is above a calibrated upper limit, or below a lower limit, for a programmable period of time an idle speed performance fault will occur.