Theory Of Operation
WARNING: This page is about a different car, the 2015 Fiat 500. 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 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 or below a calibrated upper or lower limit for a programmable period of time, and is not changing, the system is considered failing.