Hang in there, it sounds like you are making progress at least. Keep in mind that the stock ECU took much engineering to get right initially, and you are trying to replace most of its functionality. It does not come easily, but the things you are learning here apply to most every car on the road. You may have noticed that a good bit of the old school mechanics are bowing out with statements like "I can fix a car, but I not when all these computers get in the way"... or something like that. That is because it is not easy... you are attempting one of the most difficult parts of working on cars that most people pay a professional to do.

Now that that is out of the way...

You might try disabling Acceleration Enrichment, and be sure EGO control is turned off for initial testing. At least, that is my approach... limit the system to as simple as you can get it, then enable features one at a time making sure they don't mess it up.

For the IAC, are you sure your ECU has the proper jumpers in place to run the IAC? Your vendor would have set it up this way. There is an IAC test mode that I went through in my video, but it is not that great. When you power on the ignition, you should see it move to 'home', then move to where it is set to go in the IAC steps table for your current engine temp. After that, it will close further and further (with the 'base' IAC steps table) as the engine warms up.

You might also check the log for warm up enrichment if you have not. It will add fuel while the engine is cold to keep it running well, then get back to 100% of reqfuel once you are at operating temp.

I don't think your studder on throttle problem is the IAC though. Once you open the throttle blades it basically bypasses the IAC. Having a stuck or non-functional IAC that is half open is just like cracking the throttle blades a bit or using an idle air screw to adjust idle speed.

I wish I could give more advice, but I'm basically at the same point you are, only my stock ECU is being a Bitch right now. I don't have any time to work on it right now, but as I try more things I'll post more videos (hopefully).