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No probably not the IAC valve, the surging means its working and computer is using it to try to correct for a stable idle.
After engine is fully warmed up and idling, unplug the 2 wire connector on the IAC Valve
RPMs should drop about 500, barely running engine, or engine may even stall, either is GOOD, it means no air/vacuum leaks
If RPMs do not drop and/or surging continues then you do have an air leak
If you haven't changed PCV Valve in a few years then I would check it and maybe replace it.
PCV Valve is vacuum operated via its larger vacuum hose to the intake, and if its dirty or sticking it can cause the surging.
You can plug the PCV valves hose and see if idle stablizes
"In Gear" the engine now has a Load on it, so vacuum in intake changes, its not unusual to notice idle variations in Neutral, vs Under Load
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