I didn't look at those threads, but the function of the idle speed valve is to bypass enough air to bring the idle speed up to spec. If idle speed is high with the no voltage to the valve, then the only way the valve could be involved is if it were stuck open - very unlikely. The idle speed control is be doing exactly what you would expect.

Look for a 'vacuum leak', though most likely you will find it as a ruptured larger diameter rubber air supply hose in the idle speed control circuit. If you find such, carefully locate and replace ALL the rubber in the idle airflow circuit, as it will all have hardened and probably break working with it (rather like repairing a problem in galvanized steel house plumbing).

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7