Idle Learn Procedure

[100R1]

I have read several post of late about doing the Idle Learn Procedure after doing work on different components that require you to disconnect the PCM and/or power from the battery.

 

What are the correct steps in this procedure ?

[AZ1500]

The easiest way to do this is to just drive your truck around town for about 30 minutes, and every 5 minutes or so, stop, turn off the engine, wait a minute then start up and drive again for 5 minutes and repeat the procedure. You will notice that after each stop and restart, your idle will increase slowly until normal idle and fuel trim is reached.

[JayMan]

You will need to check the official Shop Manual as this procedure can change. For 1999/2000 year PCM's, do the following (Page 6-2037 of the Helm manual:

 

1.Make sure the HVAC is OFF and all other accessories are OFF.

2.Set parking brake with trans in Park.

3.Start engine and let it warm up to normal operating temp

4.Put foot on brake and shift into Drive for 5 minutes

5.Keeping foot on brake, shift into Park for 5 minutes

6.Take foot off brake and shut off motor

7.Wait 30-60 secs and restart. Idle should be normal.

 

GM does not recommend doing this by driving around. First, if you have serviced the IAC, the idle could be abnormally high (+1500 RPM) and you could get into an accident. Second, there will be weird shift characteristics until the base idle and fuel trims are stabalized.

 

This is also a good procedure to follow if you do the following: change the O2 sensors/cats, change the plugs, clean the TB and/or IAC. Once the base idle is stable, then the PCM will reliably calculate the proper long-term fuel trims.

 

The drive-by-wire Vortec's for newer model years probably have different procedures. You really need a shop manual in this case.