2002 Buick Century Idles very high and the engine races higher the longer the car runs.
First…have your codes read. If there is no code then it’s probably a bad TPS. My aunt had this same problem on her Buick and it turned out to have a bad PCM.
Locate the Idle Air Control valve on the throttle body.
While the engine is idling fast, take the handle of a screwdriver and rap on the IAC valve. If the idle speed changes, replace the IAC valve.