Idle Air Trim

PURPOSE
Idle Air Trim is designed to adjust the Idle Air Control (IAC) calibration to correct for wear and aging of components.

OPERATION
When engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The Idle Air Trim values are stored in a table for reference. This table is used by the Powertrain Control Module (PCM) as a correction factor when controlling idle speed. The table is stored in Keep Alive Random Access Memory (RAM) and retains the learned values even after the engine is shut off. A Diagnostic Trouble Code (DTC) is output to indicate that the Idle Air Trim has reached its learning limits.

RELEARN PROCEDURE
Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that Keep Alive RAM be cleared. This is necessary so the idle strategy does not use the previously learned Idle Air Trim values.

To clear Keep Alive RAM, refer to Testing and Inspection / Procedures / Powertrain Control Module (PCM) Reset (Clearing DTCs). It is important to note that erasing DTCs with a scan tool does not reset the Idle Air Trim table.

Idle Air Trim Learning Modes Chart:

Once Keep Alive RAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as the strategy adapts. Adaptation occurs in four separate modes shown in the table provided.