This helped my idle a lot
 

My car idled perfectly first thing in the morning, but got heatsoaked and idled crazy lean anytime I stopped. Sound familiar?
Searching around I found some very informative posts on Hot IAT Idle like this one. So I messed with the "IAT Corrected" setting in the "Coolant Related Air Density settings" menu but the correction seemed to be linked only to the coolant temperature.
Finally I found this thread on the msextra board that fixed the problem.

Basically, open up the msns-extra.ini file and find this bit of code:
Change xBins line to read:
Now corrections are linked to IAT as opposed to CLT.

So far so good. Sensor still heat soaks, but I'm able to compensate to maintain a good afr.

Hopefully this helps someone.

Where is your IAT sensor?

I've got the same issue except the IAT readings really do not increase drastically which is weird. If I go shopping and come back to start the car within 15 minutes or so the IAT reading is only up maybe a couple degrees but the AFRs will be off the charts lean for the first minute or so of driving. I've tried shielding the pipe until I have time to move the sensor but that didn't help and it seems like the IAT temp should have to increase much more than it does to produce the lean idle?

Intake manifold is heat soaking on you.

The option for AIT corrections is part of the standard code, just go to advanced options and select it. That's all you did, but you did it the backdoor, nerdy programmer way. I'm certain 90% of here already use it.

It's been discussed here in depth. The MSPNP map unitizes this table as shipped. Easiest solution to the problem is moving the AIT sensor out of the engine bay. However, with corrections I never really had an issue.

Nevermind, beaten.
-------
Moving the sensor out the engine bay is an interesting idea.

I think you misunderstand what you changed in the ini. All that does is make the graph show mat instead of coolant. It doesn't change anything in the megasquirt itself... so it's not going to change the way your car runs.

Well, Even when I changed the "Correction based on:" to "IAT corrected", the corrections still seemed to be CLT based. Only when I made the changes to the ini file did it work properly.

My idle is awesome now.

YMMV

I had this problem on one of my turbo datsun's. The AIT corrections helped but did not fix the problem. It only made megasquirt not change the pulse width as much. I was still seeing way too high IATs which took 20-30 seconds to get back down to correct temp. Which by then the 1/4 mile was over. My problem was the IAT was behind the radiator. I moved it closer to IC outlet and infront of the radiator and it was completely gone.

weird, ill take a look at my .ini file next time just to see if mines correct, but the corrections always worked for me, as i was seeing over 120*F intake temps on a warm day. Now my AIT remains ambient and i don't even use corrections.

Yea, weird is right.

I have been having some heatsoak issues since the winter started, almost like the megasquirt doesnt even pay attention to the bins. I wonder if for some dumb reason its paying attention to CLT instead of IAT out of no where.

It seems strange to me that the MSPNP base msq, corrections are turned off by default. I can understand you'd probably want it off during tuning, but I'm surprised the DIY install guide doesn't mention IAT corrections at all. I suspect most of the BEGi and probably other kits too, have the IAT mounted where heatsoak will be a problem.
I'll probably move the sensor eventually but this has solved my problem for now.

Before I made this change, I felt like a fool having to rev the motor just to keep it running.

the 90-93 base map has them on by default.

Wow, you're right. I wonder if this is an oversight on the 94-95 base map.