IACV repair
As a car dealer I've had several Civics that had the idle go high and then low after being warmed up. The latest was a 97 Civic DX. To solve the problem, I removed the throttle body, removed the IACV from the throttle bottle, then I unscrewed both ends of the IACV. With the shaft exposed, I was unable to easily rotate the shaft. I sprayed some Powerlube on both ends and worked the shaft back and forth by hand. After a while it freed up with just a little resistance. I replaced the end pieces and then reinstalled the throttle body. It had one up and down cycle, and then settled in and idled perfectly. It was quite a relief to solve the problem so inexpensively. Before doing this I had replaced the IACV with another one I had from another engine. It did the same thing. This, I would guess, is a common problem, especially with engines that may sit for a while unused, which both of these engines had.
DH