If the only problem is when it's idling, it is probably the IAC valve, which stands for the Idle Air Control valve.
They can be cleaned, but it's a little bit of a PIA to get at it, since it is behind the throttle body horn.
Just follow the small plastic tube that is connected to the intake tube in front of the throttle body. When you get to the other end of the plastic tube, you should find the IAC
Steve - TCCoA member
2003 Crown Vic LX Sport
1995 T-Bird LX 4.6 retired at 247,888 miles
Thanks for the ride !