My 1989 Ford is idling too fast, and the choke does not seem to open when the engine gets warm. I have changed the IAC valve. This did not change anything. Suggestions?
High Idle is a clear sign of a vacuum leak. Check the PCV hose first as it is the most common.
A failing ETC Sensor or unplugged sensor may also make the vehicle not want to come down off choke. It would be somewhat picky wanting to restart after it was warmed up. You may see excessive smoke at that point if this is causing the issue.
What Should I check?
It would be a great idea to check for any existing codes. Especially since you do not need a scan tool to check the codes.