High Idle... Dealer is worthless... Please Help

I have been dealing with a high idle since I bought the car. After having it into the dealership on noumerous occasions, they finally ordered a new ICA for it. Well it took them two months to get the correct Idle Control Assembly. They put it on yesterday, and if anything the idle is higher. The mechanic told me that mustangs just idle high, BS. IT is idling around 1200 rpms at a stop, and some times it goes as high as 1700 rpms. Do you guys have an ideas on what it could be????? Do you guys have any more ideas on how to get my dealer to pull there heads out of there arses?????

Thanks in advance.

Doug