I have a 68 Camaro with a 93 LTI 350. I used a painless wire harness and a 93 PCM. I’ve had this combination for several years and has been running fine. Lately I’ve been have trouble with the idle . I can reset the IAC idles fine for 2 or 3 minutes then gradually keeps getting faster, up to about 2500 rpm and that’s where it stays till I rest it. Any ideas replaced IAC ,cleaned throttle body checked wiring.

 

Any trouble codes? How are you resetting it?