One possibility is a bad engine coolant sensor. It may tell the computer the engine is warm, when in-fact its cold. This will cause the computer to misadjust the idle control.
I had a similar problem with my car recently. I have the wiring diagram and was able to diagnose it by measuring the resistance of the coolant sensor and determining that-its defective. Changing the sensor fixed the problem. My car, unlike yours, provides very limited engine codes. Defective coolant sensor is however one of the provided codes. However I also had no error codes whatsoever.
Perhaps someone with a wiring diagram for your specific car can help you out. Alternatively, as a substitute to the service CD you may want to subscribe to "ALL DATA" -
http://www.alldatadiy.com/ - its around $25.00/year/Model car, and has the same info as the service CD. That's where I get most of my info, including diagnostic procedures, electrical wiring diagrams, etc., etc..
Much cheaper than having the dealer diagnose the problem.
Phil