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Originally Posted by JFAZ
anthonyb, thanks for the info.
sbourg, IAV = ICV right? So you are suggesting that everything is ok with this part right? Where do you think is the best place to look for an air/vacuum leak considering that the throttle is fully closed?
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Yes, and no. The idle air valve is an air 'leak' around the throttle valve. Air that passes through it therefore comes through the airflow meter, then back into the intake manifold. Any rupture in the plumbing that routes the air in this path will allow non-metered (and unfiltered) air to enter the manifold. Further, if the leak were between the idle air valve and the airflow meter plenum, the valve should still be able to control it - and this appears to not be the case. Most likely, then, is an air leak in the plumbing leading to the intake manifold.
My experience with this vintage is that all the rubber air plumbing will have hardened, possibly cracked, but in any event seal poorly at all connections. It will also certainly disintegrate if you attempt to remove it. Best procedure is to order all new plumbing and replace it all at once. This includes the branch that goes from the manifold to the breather port on the valve cover - the part that is between the pcv orifice and manifold also causes problems.
Note that none of this absolves the idle air valve, but you can't judge it until the air leak is fixed, which will likely solve the problem.
Steve