2002 Accord 2.3 (Automatic->Manual)
So recently engine swapped, my F23A4 went out on me and got a F23A5 with low miles to replace it about a month ago. The car runs perfectly normal while driving, and even when I hit vtec at 4200 rpm, but after going into neutral after hitting vtec the rpm drops to about 300 rpm causing a very rough, slightly shaky idle and sometimes when I stop at a light after that it will shut off. If I restart the car while rolling or stopped, it acts perfectly fine again, idling smoothly right below 1000 rpm.
(Cold starts do sometimes need a little steady gas to keep it on, but honestly it seems like the problems are unrelated. Giving it steady gas to "train" it to stay at 1000 does not help after vtec. Plus like i said when I start it back up after the rough idle at vtec, it runs perfectly fine)

I've seen other forums similar to this suggesting iac valve problems, but after Web researching I'm not completely convinced. If anyone has ever had this issue, or heard of it happening, I would love some insight. Thanks.