Have you set the "minimum air rate" setting?
If not, the idle can hunt all over.

Also the more sensors you have, in respect to the same engine in an GM OEM application the better.

No Vehicle speed sensor (VSS), No Brake switch, No Park neutral switch, no air charge temp sensor? If not, get them. You may have to have the ecm prom reflashed.

Min air setting...air cleaner off, right above the IAC (Idle air control motor) on the side of the TB, is a vacuum passage, (snap on makes several special tools to do this) but a shop towel stuffed into that passage will effectivly block the air passing through. The idle should come way down, if not stall when you block that passage. While blocked, (unseal, if not already)the idle speed screw (torx) and adjust the idle to 400-500 rpm (trans in neutral).
Then pull the passage plug, shut off the engine, clear the memory (dissconect the battery for 30 minutes)restart and drive at least 2-3 drive cycles. A drive cycle is...start up drive for at least 5 minutes and during get to above 35 mph for 10-20 seconds then stop, shut off engine and repeat. If you have no VSS just drive for 20 minutes.

The IAC motor should relearn to set the idle speeds.

SD