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.