IAC question

[larrym]

So what other information other than rpm does the computer use to calculate IAC counts?

 

[RmvBfrFlght]

I take it you are referring to idle. The P/N input to the ECM is used, there are two idle speed tables. One for in drive and the other for P/N.

The two tables of desired idle speed is based on the engine coolant temperature (CTS). So an incorrect CTS reading will affect the idle speed.

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[larrym]

Sorry yes idle.
I been chasing a problem that I originally thought was a large vacuum leak eventually found my IAC was cycling at 150 that's why it was so lean at idle.
I have reset the IAC by putting it into Diagnostic mode and unplugging the IAC tried a different ECM different chip different MAF sensor finally traced to my MAF translator.
I'm just trying to understand what sensor information is used other than RPM to control the IAC.
Some times it starts and it's all good the next time it is mental.

 

[larrym]

Ok here is a data log showing what my RPM and airflow in and AFR when it goes mental. The scan tool data is off my autoXray tunerPro only displays the data the GEN2 uses.

Note the MAF in.

Here is the next time I fire it up right as rain disregard the audio [emoji38]

Lower MAF reading smooth RPM and AFR is normal IAC if normal.

 

[dank GN]

Did u adjust your IAC correctly? You open the throttle blade to lower them and close it to raise them . Then of course you have to reset your TPS. Also what's your fuel pressure set to?

 

[larrym]

I have narrowed it down to the translator.I think.
I have swapped fuel pumps, tried a known good computer different chip reset the IAC adjusted the crank sensor the only thing that smartened it up was a different translator and chip.
I'm just trying to wrap my head around the problem. How does a MAF problem affect the IAC at idle.

 

[RmvBfrFlght]

How does a MAF problem affect the IAC at idle.

If the MAF is reporting incorrectly the engine will struggle to run. It will be either too lean or too rich. At idle the ECM will open the IAC for more air to keep the desired idle speed. I'd say that the high IAC counts a symptom, not a cause.

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