Short Term Idle Trim and Open Loop SD
 

Can the two play together well?

I have a stumble at hot idle when both fans kick on where timing will plummet and the motor will bog trying to maintain electrical load.

not really addressing you main question but...
would a time delay relay work by allowing one fan to turn off a few seconds after the first, or would even one fan turning on cause the issue?

They are not both commanded on together but a hot idle, and when both are on the idle sometimes bogs. Only thing it can be is bad battery/alt, or tune. I know bat and alt are working, so leaves the tune. STIT is whats used for AC high idle command etc, from what I gather. Should be just small tweaks to keep a clean idle.

You're using a 411 PCM correct?

STIT is an idle short term trim similar to short term fuel trims, whereas it's not commanded in the tune but is rather a trimming based on the commanded base idle airflow and what is actually needed to maintain commanded idle.

Need to see if your ignition timing is dropping as a result of the idle rpm going down or if the idle timing drops first, then the rpm dips. Depending on what year OS is used in your car, there is a table that can be adjusted that controls how much timing is removed when the AC command kicks on, although that's different from just a second fan engagement setting.

Yes, 0411 PCM, believe its an 2002 and 3bar OS.

I know short term fuel stuff is long gone since its OLSD but I believe the idle trims should still be used?

I just want something to let the tune catch itself quicker when the electrical load spikes, similar to the AC being engaged, if that makes sense.

That makes sense, timing is actually the quickest way to catch/control idle since the iac is slower than a change in ignition advance.

You have HPT right? Do you have a log of this happening?