IAC motor just need time to learn?

My new 383 will Idle fine just sitting but when i'm on the road and push in the clutch to coast or roll to a stop the car idles lowww, then dies. I have a BBK 58mm TB and made the modification where you drill the hole for the iac...did this help or hurt? i'm not sure, i did read in my haynes manual (it was good for something!) that when disconnected the ecm needs time to relearn the idle speed of the engine...should i not worry about it and give it time, or look and check something else?

This belongs on "Computer...", or "LT1 Tech".

There is a "learn" precedure for baselining the IAC target counts. Shoebox has it on his website. But that doesn't sound like the problem you are having. IAC counts on over-run (coasting on closed throttle) is controlled by a seperate table. Perhaps your prgammer needs to make adjustments to that table.

Moving to "Computer...."

Sounds like a vacuum leak to me.