Actually, rpm dropping from a high value is a tough thing for the idle control system. It needs to have all it's stuff adjusted right. The ECU has to know how & when to open up the IACV in anticipation of the RPM dropping to idle. If it waits for the RPM to reach 750 it's too late because it takes many milliseconds for the IACV to open & by that time the RPM is low enough to stall.

IACV cleanliness, IACV response speed, TPS adjustment, & idle-air bleed screw adjustment all influence that. If you have used one thing to compensate for mis-adjustment in another thing, it gets all messed up.