[Flatrater]

I would look for vaccum leaks on the engine! Most high idle problems are caused by air entering the engine downstream of the MAF sensor.

Every tech has a different way to tackle the problem, no one way is right. GM does have a general guideline trouble tree for your code but most techs thru experience learn quicker and easier ways to find the problem.

To you it should be more important that the dealer finds and fixes the problem then how they find the problem. Most techs do not like people watching them to learn hoew to fix a car, so be nice ask any questions you may have and let them fix your car!