You were asking about sensors...i'm sure you already tried this...but I did a Google search for "high idling" on the 90 t bird...came up with a few articles that talked about something called a Mass Air Flow Sensor ---- but the symptoms it described seemed more geared toward lower idling...sputtering etc. & only way to fix it is to replace the sensor....

But also came up with a number of articles and service bulletins from Ford about the "Throttle Air Bypass Valves"...sypmtoms included High or Low idling...