I have a 1990 Ford F-150... 5.0 with 163,000 miles. My engine started idling high, 2200 RPM when first started. I replaced the idle control valve. I still have same problem when first cranked, it idles @ 2200 RPM and then will gradually drop to 1200 RPM. What do I need to do next?
Thank you

Note steps 4 and 6 in the link below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-7.html#post1054149

If these hoses and passage ways are clogged, the new IACV won't be able to work properly. It's amazing how much dirt can build-up, particularly if air filters are not changed regularly.

If all of that seems fine, you may just need to adjust the throttle cable.

I don't know if this would apply to your truck but my car does the same thing and I found out that it was one of the fuel injectors that was bad.

Other possibilities:

. Check Fast Idle Thermo Valve, if any.

. Check/replace Engine Coolant Temperature (ECT) Sensor, which affects fuel injector pulse width. It's normally located on the thermostat. The ECT Sensor is a temperature dependent resistor (thermistor), whose resistance decreases as the engine coolant temperature increases. It provides a richer mixture when cold, leaner mixture when hot.

Good job.