IAC note sounds like vacuum leak

check for a vacuum leak like broken hose/off etc. also, check fuel pressure with a gauge auto parts rent it. check for duct work between air cleaner and engine for holes/ off. See link.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check over all the vacuum lines, especially the ones that run through the firewall, with that many miles you may have a cracked/broken line. Very easy to knock one off.