Can you list your engine mods?
If the engine has a cam, it sounds like the running airflow table is way off. If that's the issue, you're pedaling it until the computer can adjust the IAC far enough inline to let it idle.
On a slightly related note, if you're waiting on payday's to throw more parts at it, you really need to stop blindly buying parts to try and fix it. What you're describing sounds very tune related to me.
05 Quicksilver Twin Turbo GTO
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