no, the fact you have vac. advance hooked to manifold vaccuum, and at 10" you're partially on the advance curve is why. when you're at higher RPM it has more vac. advance because it's pulling more vaccuum. but as RPM drops in the idle range, vac drops, so timing is pulled out, making RPM drop more, and it continues to spiral down until you're back (probably) to base timing. switch your vacuum advance to ported vacuum, and your unstable idle return/excessive in-gear idle drop will go away.