Real low desired idle airflow

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My car idles pretty well i just have an issue when the car gets hotter or mostly when the IATs are real high it will just keep wanting to pull idle airflow.

It will pull desired airflow down to high 6 g/s in gear and 4s in park.

The other thing i noticed is when shifting into park or into drive the rpms will jump as the pcm commands 10.5 g/s that the tune wants, then hang for a few seconds and come down as the IAC closes and brings the airflow down.

Now common sense tells me that the BRAF is to high but before the IATs get so high the idle trims are not bad amd i dont get that hanging idle. And i no way will my cam want 6g/s at idle when dynamic is closer to 15-16g/s.

Also thinking it may have to do with IAC vs Effective area as my dynamic airflow never matches my desired. The iac vs eff may be off causing issue?

Im not near my laptop but mods are in sig.

[A.ROY]

What if you were to change your cylinder charge temp bias more towards coolant temp? Mind you, I am in the middle of tuning my first fuel injection ride as we speak, so real new to all this. I do know I had to change mine, but I'm running speed density and have my maf hooked up just to have the intake temp sensor absolute to the pcm. I have it up by my headlight in the engine bay. Mine is a cammed 4.8 in a Lexus IS300.

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I have it right in the middle so there isnt a whole lot of correction. Not always the best way but going with it.
Sometimes it will come to idle a few points richer but eventually smooth out.

I came to think about IAC vs Effective area since my desired and dynamic airflows do not match, tho my maf and dynamic are relatively smilar.

For iac i was using a spreadsheet but the results didnt seem to make sense.


Im using a formula i found online to let the scanner do it and the results seem much better.
So if the iac vs effective area is off i had to reduce it a whole lot. I com
I havent tested yet b

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So thanks to youtube i made an IAC vs effective area correction graph.

I had to modify the table A LOT.
brought my desired and dyamic airflow hell of a lot closer.

I didnt drive it but the hanging idle switching gears didnt seem to be as prevelant on second start up.

I made a BRAF table and the trims came into line.

Only time the trims started pulling a lot of air is when the IAT got to about 115?.

When the IAT lowered the trims started coming closer into line.

So i guess ill just modify this table to reflect normal IAT range. Typically under 100 then let the pcm do the rest. As IATs only come up sitting in traffic or somthing.

[ChopperDoc]

Awww, I was just going to refer to such a video... Looks like you found it. I’m really glad it helped you out either way.

[anniversaryss]

Awww, I was just going to refer to such a video... Looks like you found it. I’m really glad it helped you out either way.

It absolutely did. I still got to do a few more logs to smooth it out a bit but its doing well at the moment.

I guess the differences in the throttle bodies and IAC between lt1s and LS1s make a real big difference in this case.

[ChopperDoc]

Awesome. Just remember that when the IAT shifts around, the numbers can be off, as in they might match when you tune it, but they won’t the next day, etc.

The idle calculations are different from the airmass calculations, and have some sort of modifier, but using dynamic to dial it in still works better than the spreadsheet if you ask me. The PID “Desired Airflow” is actually the IAC Effective area in the tune. I still haven’t figured out the conversion for it, though I did take a crack at it, but as of now all I can say for certain is “idle desired” and dynamic air are not the same, however, they do follow a logical curve, therefore dialing in the desired to dynamic will get it closer to reality. The numbers will vary from then on, but so long as the counts are good, as in 40-60 hot, then it will warm up okay, and shouldn’t give you issues.

Long story short, don’t overtune it... just get it stable and call it good lol. Ask me how I know hahaha

[anniversaryss]

Awesome. Just remember that when the IAT shifts around, the numbers can be off, as in they might match when you tune it, but they won’t the next day, etc.

The idle calculations are different from the airmass calculations, and have some sort of modifier, but using dynamic to dial it in still works better than the spreadsheet if you ask me. The PID “Desired Airflow” is actually the IAC Effective area in the tune. I still haven’t figured out the conversion for it, though I did take a crack at it, but as of now all I can say for certain is “idle desired” and dynamic air are not the same, however, they do follow a logical curve, therefore dialing in the desired to dynamic will get it closer to reality. The numbers will vary from then on, but so long as the counts are good, as in 40-60 hot, then it will warm up okay, and shouldn’t give you issues.

Long story short, don’t overtune it... just get it stable and call it good lol. Ask me how I know hahaha

Good explanation thank you. I didnt know that desired idle airflow was actually IAC airflow but thinking about it, it makes sense.

What my plan was, was to get my BRAF as close to what i would normally run as far as IATs go.
Then just let the trims take over. It all make sense now why my desired flow was less at high IATs. But i suppose now i know and ill just tune around it.

Thank you for that information. I might be rambling now bc im tired haha.