Idle control question

[John377]

Can someone explain to me what controls the idle from cold start until the temperature that is set for Adaptive idle learning. Is there a reason to not set the adaptive idle learning temperature to a lower temp than normal operating range, say 176?

I live in a cold climate and it takes a long time for the engine to reach full temperature in the Winter. If I drive prior to full temperature I get a condition of the idle dropping below the set RPM and then has to fight its way backup when coming to a stop.

[kevin87turbot]

What application do you have?

[John377]

Gen 3 P01. 2002 chevy silverado 6.0

[kevin87turbot]

What mods are done?

[Matt Vardaman]

The Idle Rpm table controls desired Rpm. Ignition advance is used to control Idle quickly, and the Idle Air Control valve moves more slowly. It is my understanding that the Idle adaptives i.e. Long term idle trim and short term idle trims are a PID loop (proportional, integer, Derivative). They would Primarily affect the IAC to allow more or less airflow to achieve desired Idle rpm/airflow.

[Matt Vardaman]

You could have an IAC on the way out, dirty throttle blade, or another mechanical problem. Has the Vehicle been tuned already or is this a stock engine?


When my Iac valve was failing. It slowly started to want/try to die in gear. It had been running perfectly before for around a year. So I knew it was not in the tune file. Proper Diagnosis is everything.

[John377]

Thanks for the response. I think i got a good idea of how all the systems work. Im just a little confused as to the warm up period. It seems to be, "handing off", to different tables as it warm up. It runs great once warm, just that little rpm drop when comming to a stop in gear before full temp has reached.

Ive done a lot of idle tuning and my trims are very low.

It is an SD tune
102mm TB on 102 Fast LSXRT intake
78/76 turbo
04 z06 cam

[John377]

Thanks ill check this. Its new but ive had a lot of new bad parts

[Matt Vardaman]

Until it reaches 131 degrees its in open loop. There seems to be a cold startup protocol that we can't see, with my Autel scantool it shows a flag for Cold Startup Yes/No. Do you have your Open loop short term fuel trims enabled? or are you running SD Openloop all the time?

It could also be something minor like a partially stuck open thermostat. The new bad part problem seems to be getting worse.

[John377]

Open loop short term trims are disabled, but ive tried it enabled with no difference. The problem occurs in open loop before 131 as well as closed between 131 and 170 which is where i have the adaptive idle learning temp set.

[Matt Vardaman]

If you can get a log of the problem, we might be able to help further. Without that, we just guessing.

[John377]

I appreciate all the comments I didn't want to turn this into a huge thread. I was just hoping someone could direct me to the parameters that control the idle during the temperature ranges I was asking about. Prior to adaptive idle kicking in.

I've logged it I can see the dip and I can see if fight its way backup I just don't know what part of the program is doing this. Are the adaptive idle Parameters working prior to the learning temperature, it's just not remembering them?.

[The Black Sheep]

Adaptive idle works once the ETC min is hit. Before that, all values to get your idle stable are in STIT and are not stored in the LTIT until the ETC is met. Log LTIT in gear, LTIT in p/n, and STIT. Do a cold start and you will see STIT pick up (or remove) any airflow needed. Outside of this you have your Overspeed and Underspeed tables for faster rpm corrections. Sounds like you need more airflow in gear.

[John377]

Thank you, that helps i will do that in the morning.

[John377]

Thank you for pointing me in the right direction. I found where the error occurred. In my original idle tuning it appears that I inadvertently had my graphs settings in Celsius and then pasted them into my tune under Fahrenheit.

[The Black Sheep]

Glad we could help