Idle Relearn

[SappySE107]

A new page entry has been added:

[drupal=137]Idle Relearn[/drupal]

There are a few methods floating around, but this is the one used by GM techs (OBD1 method).
<ol style="list-style-type: decimal"> Reset ECM by pulling ECM fuse (underhood) for a few seconds.
With A/C turned off, start car and immediately put it in Drive
with your foot on the brake. If the car does not start initially,
keep trying WITHOUT putting your foot on the accelerator. Idle the vehicle in Drive for autos and neutral for manuals until the coolant fan has cycled on then off for one minute.
Shut off the car for 10 seconds.

[billgraves]

Step 3 reason

Step 3 states to Idle for 5 minutes. The software in the ECM NEEDS TO SEE THE COOLANT FAN CYCLE ON then OFF to LEARN the Base IAC position for the relearn. So the step should read: Idle the vehicle in Drive for autos and neutral for manuals until the coolant fan has cycled on then off for one minute. Then you may turn it off. (from GM 60 degree Engineering)

[asylummotorsports]

All the GM techs I know just get in the damn car and go for a 15 minute drive.

Works perfectly!

[robertisaar]

All the GM techs I know just get in the damn car and go for a 15 minute drive.

Works perfectly!

more or less, that does work well enough, so long as it includes a lot of stop and go.

[bszopi]

Glad you finally decided to post, Billy. I'll get it changed one of these days...

[Superdave]

It's all overkill IMO.. I've done hundreds of idle re-learns and never had a problem with my way..

1. disconnect battery for a few minutes
2. Connect battery and try to start car.. it should stall out.
3. Re-start the car and leave it alone while it idles up and then back down. Once the idle has settled it's fine. You can watch all this in a datalog.


The ECM is just extending and retracting the IAC motor on a timer, it assumes that after it's fully extended, then fully retracted that the stepper motor counts are correct. Many industrial machines use the same logic as long as there isn't any damage to be had from over-extending or retracting the device. I see it used with electric rams daily.



it is nice to see someone from GM here though, Welcome!

[robertisaar]

2. Connect battery and try to start car.. it should stall out.

on stock tunes maybe, but i set the IAC re-initialization point a bit higher than the stock point so it doesn't die on start-up. shifting into drive can do it though. that's when i have to do above steps and get a better number to start with.

[Superdave]

I don't mess with that, If it doesn't die on the first startup then it gets all screwey.

even with the huge cam my 3500 idled like a dream. IAC counts stayed between 20 and 40 with the MAP around 60 Kpa, 1100 RPM.

[IsaacHayes]

Too bad OBD1 doesn't use the same logic as OBD1.5, it fires right up after a battery disconnect and idles perfect.

[tkoforpresident]

hmmm my "idle" hasn't learned itself even though i've let it sit and idle (irradicaly) for a number of different times. So when i get things straightened out i'll try the whole list.

[asylummotorsports]

My car idles at ~750 RPM in gear and doesn't have idle or start issues, and I have NEVER done a re-learn the way GM proposes it!

Go for a drive. Let the fan cycle a couple of times.

God knows the tune on my car is frankenstien enough to confuse anyone, but OBD-1 pics it up and the car runs just fine.

With all the crap done to my car I have never had an issue as long as you use good parts.

TCE TB, Delco TPS and IAC, and just let the ECU get used to it all.

My car will idle all day without an issue.