I HAVE A IDLING PROBLEm at engine start she idles high,when i come to a stop li on 1999 Ford Mustang

lite she idles so low it seems lt gonna shut off sometimes i shift to netural, what could b the problem plugs and wires were chsnged also fuei filter,is there some sort of idlling switch i should change

2 answers
Most likely it is the IAC (idle air control) replace the IAC clean the throttle body then clear all codes and reset the keep alive memory. Road test at various speeds for about twenty minutes to relearn the idle stratedgy.
as pure says idle air control is a common idle problem or pwr to it