1992 Cadillac Deville engine wont idle down

The car was running fine. I went to start the car one morning and cold idle seemed to be running fast and never idled down. I took to a friend who gave a quick fix adjusted idle, but computer seemed to speed it back up. I checked the trouble codes and got these.E26, shorted throttle switch circuit, e30 isc rpm out of range, e98 p/n to d/r isc engaged problem. Check engine light comes on too. Would sure appreciate any ideas to help fix this problem.