94 Cadillac STS engine problems

When I start my car, the enging races anywhere from 2000 to 3000 rpm without me steping on the gas. When placed in gear, it also tends to accelerate to around 15 to 20 mph also without me steping on the gas. What could be causing this?

I'd start by cleaning the throttle body and plates with carb cleaner and a tooth brush followed by disconnecting the neg bat terminal for a couple of minutes then reconnecting, thus allowing the comp to reset to default.
FWIW
YMMV

If that doesn't work, I'd look into a possible idle speed controller failure.