Idle Reset (again)

[Johnny_Eye]

No I'm not asking for the idle reset procedure. But I am curious. Why is it important to perform an idle reset after you replace plugs and wires? I thought the idle reset simply cleared the codes and established load maximums. Is there any additional benefit one should expect?

Thanks.

 

[NotSoSlowSHO]

Because you are supposed to disconnect the battery before attempting any kind of repare or replacement of electrical components.

Since you disconnect the battery, it must relearn idle.

 

[Rockledge]

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 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 idle speed. The table is stored in Keep Alive Random Access Memory (KAM) and retains the learned values even after the engine is shut off.

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.

Like Kenny pointed out, many SHO repairs require disconnecting the battery. This clears KAM, which is where trouble codes are stored. Fuel trim and idle air trim tables are also stored in KAM (see above), so they get cleared as well. The idle reset procedure simply speeds up the process of the PCM re-learning the appropriate idle air trim parameters for that particular vehicle.