High idle problems can be caused by the cold-start thermowax or the corresponding coolant passages for the thermowax.  The high idle is usually a very consistent 1,200RPM to 3,000RPM.

Clogged coolant passages prevent proper functioning of the thermowax by preventing proper coolant flow.  The thermowax doesn't melt, and the throttle plates are stuck in the high-idle position.  These coolant passages from from the back of the water pump housing to the BAC valve to the throttle body and eventually end going down the top of the rear rotor side housing.

If the thermowax itself failed, you'll need to replace the unit.

Questions?  Comments?  Send mail to:  reted@fc3spro.com