i drove about 70 miles on the interstate at 75 to 80 mph non stop and when i stopped my car was stuck at 3000 rpms and it would not idle down. i just bought the car a few days ago but i dont know what is causing this to happen. i started it up the next morning and it instantly revved up to about 2000 rpms and stayed there. i shut it off and about a half hour later started it and it idled normally. any idea why its doing this?