Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Idle Air Trim
Idle air trim is designed to adjust the idle air control (IAC) calibration to correct for wear and aging of components. When the 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 PCM as a correction factor when controlling the idle speed. The table is stored in keep alive memory (KAM) and retains the learned values even after the engine is shut off. A diagnostic trouble code (DTC) is output if the idle air trim has reached its learning limits.
Whenever an IAC component is repaired or cleaned, or a repair affecting idle is carried out, it is recommended that the KAM be reset. This is necessary so the idle strategy does not use the previously learned idle air trim values.
To reset the KAM, refer to RESETTING THE KEEP ALIVE MEMORY (KAM) . It is important to note that erasing DTCs with a diagnostic tool does not reset the idle air trim table.
Once the KAM 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 4 separate modes. The modes are shown in the IDLE AIR TRIM LEARNING MODES table.
| Transmission Range | Air Conditioning Mode |
|---|---|
| NEUTRAL | A/C ON |
| NEUTRAL | A/C OFF |
| DRIVE | A/C ON |
| DRIVE | A/C OFF |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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