How do I diagnose a very high idle speed problem on 1992 Ford Taurus

Idle on start is up to 2500rpm, then down to 1200rpm. I don't find any vaccum leak. Idle is 900 to 1000 RPM in gear , warm motor!!!

1 answer
There was a Ford TSB on this that basically said check the throttle cable and linkage and , if necessary , replace the idle air control valve.
Some folks simply clean the valve , inside and out......