Idling issue

[ksubclass]

So I noticed that when I shift into neutral to come to a stop from 30 or so mph to a stop the rpm will bounce up to 1600 and drop back down to 1350 repeatedly until I come to a complete stop and then once I stop the car the rpm will gently lower down to 900 or so.
Has anyone else experienced this? Also I am throwing a P0505 code and a P1140 so I'm pretty sure that has something to do with it.
I checked the ohms on the IACV and it is correct ohms for operation.

[1996 328ti]

Vacuum problems are tough yet common.

[pdxmotorhead]

First remove and inspect the host from the Air Flow sensor to the throttle body, they get old and get cracks on the bottom side that don't show up easily till you take it out and look and flex it. Then check the air hoses under the intake manifold, same deal they rot with time.