Generally, when a vehicle idles too high it's because of an imbalance in the fuel/air mixture ratio, but there could also be a lot of other things. Have you checked the oil? If it's low on oil, it could be partially at fault. Also, when's the last time you went to the dealership and had regular maintenance done? Sometimes, the mechanics can offer and insight. I hope the situation gets resolved for you!
I had a dirty linkage on a 95 SC2 that caused a similar high idle and revving. It took the dealer a couple times to clean and lube it before it stopped.
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