Blue Hawg

OK here's the deal. I recently ran across a clean 2000 Civic EX for a price I couldnt pass up. Now that I have the car i have learned some stuff about it such as,,,, it's a 2000 with a '95 D16Z6 engine. Not sure if the tranny was swapped (has a 5 speed MT) but i'm pretty sure neither the ECU or wiring harness were swapped. The problem I am having is an idling issue.

When I start the car it hits around 1.5 to 2k RPM with no load and then will drop to 750 to 1k. When i drive down the road and come to a stop it will hang around 2.5k RPM for several seconds (5 to 15) and then drop back down to around 1k or less.

I am guessing this is not normal for the car and not sure where to start to try and fix the issue.

Is the 2000 ECU for the D16Y8 compatible with the D16Z6 and would resetting the ECU possibly help the issue. Im gonna clean the FITV and see if that helps. Not gonna mess with the IAC for now as the engine temp doesnt seem to be an affecting issue. It does the same thing hot or cold.

Anyways I would really appreciate any advice offered as I am new to the Honda World. Thanks In Advance

Ps: the engine runs very smooth, no missing or hesitation, just the slow idle drop down.