Could this idle phenomenom be the result of a bad gasket around the intake mani? When it warms up the leak reseals? Just thinking out loud here so bare with me. I have also heard of problems with the ISC (or IAC) in other cars... like Hyundai's, where the internals actually corode over time and result in unhindered air flow through the ISC. Since this seems to be an elusive prob, and seems to be happening on the older DSM's, I just thought that I would throw some thoughts out there for all to consider.
A.