O2 Correction at Idle or something?
 

This weekend, in preparation for a turbo, we installed an LC-1, ripped off heat shields and such things in the engine bay (to give a better idea of what we had to work with for manifold making), and put in a new clutch.

Now, when I start the car after it's hot, it runs fine for a few seconds and then as soon as the LC-1 starts sending a signal it gets lean. Sometimes it even dies. Sometimes it only goes a little bit lean, other times it goes VERY lean.

I have EGO correction set to off below 1500rpm, so I don't understand what the problem is.

FWIW, my intake temperatures are a little high because of the missing heat shields. Could that cause this? Does IAT have a correction, and if so does it wait for a signal from an O2 sensor before coming on?

I attached my latest hot-start log and msq for good measure, but it barely did it this time. For some reason the O2 never started on the first start, so I shut the car off and tried again.

Re-reading this post, I feel like a dumbass but I don't know the answer so I guess I'll pretend there are no stupid questions like my mother used to say and ask anyway.

either you have your idle cells too low in your VE table or you are heat soaking the sensor which causes it to report higher than actual temps which in turn leans the fuel out too much for the actual density of the intake air. If the latter, 2 ways to deal with that. Move your IAT sensor to a cooler place and/or enable the IAT corrected air density trim.

read this thread https://www.miataturbo.net/forum/showthread.php?t=24976

and this one https://www.miataturbo.net/forum/showthread.php?t=11659

I read all about heatsoaking the metal GM sensor, but I still have the stock one with the stock airbox.

I play with the VE table and it helps, but why does it wait for the O2 signal before it goes lean?

It doesn't. It's coincidence maybe. Your car is in after start enrichment mode when you first start it. Are you using firmware with the correct easytherm values for your stock AFM/MAF? With IAT temps in the 150's I think you should look into shielding your intake box/snorkel.