91 f-150 fast idle 1400rpm
 

have replaced idle control valve - and throttle plate sensor - still idles fast

Does it eventually drop to 800 if you let it idle for 5 minutes?

What about in drive, when you put it in drive does it drop?

This is in the wrong section, you'll have an easier time getting a reply in the f150 forum, although it's a pretty general topic.