they usually become carboned up and then the extra forcd the iac is trying to use to close and open it with all that shat on there will hurt it. Usually you can clean them and be ok. If not, then replace it.
Once you reset the computer, it should take a little while for it to learn the idle.
Final setting should go something like this:
get the timing close, enough for it to run ok. let it warm up till the fans come on. Set base idle. then, trip the computer and then set base timing. your idle should change. after you have base timing, un-trip the computer and set final idle. always make idle adjustments at operating temp. since the iac takes care of high idle when its cooler.