I believe your are speaking of the IAC (Idle Air Control Valve).
What exactly did they say needed to be done? If the person your sold it to had a diagnostic done they should have a readout of what needs to be fixed. If not ask them to get one. Cause if it is just the IAC then it shouldn't cost anywhere near that.
Here is a pic of the IAC.... may not look exactly like this one but it will be close... This one is for a 97 explorer...
Monday, March 30th, 2009 AT 6:02 PM