Low idle at stops, only after the car warms up.

This problem was diagnosed by 2carpros as possibly the IACV, however I didn't mention the idle became low only after the car warms up. The pepboys shop diagnosed the problem as a leaking manifold gasket. Does this seem right, after taking into account the warmup condition, or is it the IACV afterall?

Thanks for your expert help.
jwpoz