The only way I know to check one would be to compare its resistance (across its range of positions) with a new one just out of the box. But if the old one tested good I would likely replace it anyway - and keep the old one as a spare. At
www.rockauto.com they list them from $27 up to $43 dollars, plus shipping cost. I dont know that I would buy the cheapest one though.
They list the idle air control valve (in the fuel/air parts listings) at $34 & $51, plus shipping cost.
Good Luck....