Idle Air Trim

Idle Air Trim is designed to adjust Idle Air Control (IAC) calibration to correct for wear and aging of components. When engine conditions meet learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. Idle air trim values are stored in a table for reference. This table is used by 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 engine is shut off. A DTC is output if idle air trim has reached its learning limits.

Whenever an IAC component is replaced or cleaned or a service affecting idle is performed, it is recommended that RAM be cleared. This is necessary so idle strategy does not use previously learned idle air trim values. To clear RAM, see KEEP ALIVE RANDOM ACCESS MEMORY RESET PROCEDURE under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article. It is important to note that erasing DTCs with a scan tool does not reset idle air trim table. Once RAM has been reset, engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality will improve as strategy adapts. Adaptation occurs in 4 separate modes. The modes are shown in IDLE AIR TRIM LEARNING MODES  table.