idle on car races from 700rpm to over 1000. on 1999 Ford Mustang

when car is started engine races and then cuts down to about 700 rpm. when driving and then stopping at destination car races so much (over1000rpm) when putting car in reverse it kicks in hard. is there an idle sensor on this vehicle or is there something wrong with a choke.

Asked by for the 1999 Ford Mustang