MD-83
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
Departing FL220 descending; it was noted L oil temp at 199 degrees.  QRH was completed; throttle idle gave an immediate (1-2 seconds) to 109 degrees.  Increasing throttle to 1.1 gave an immediate rise in oil temp indication.  Fuel temp (7 degrees) and oil quantity were normal for this phase of flight.  Fuel heat was not selected or on.  Opted to leave engine running at idle; as I felt it more prudent to have the engine in the event we needed increased performance.  An emergency was declared due to idle thrust on one engine.  Communicated with flight attendants what was going on; but did not advise them to prepare the cabin as I had not turned fuel lever off.  I spoke to the passengers on the ground that we were having the emergency equipment take a look at us; as we had an abnormal indication on approach.  While SE approach checklist was completed; throttles were not matched due to above.  I advised the First Officer I would land the aircraft.  An uneventful approach and landing concluded the flight.
MD-83 Captain experiences a high oil temperature indication during descent.  Reducing thrust to idle produces an immediate 90 degree temperature reduction and adding thrust returns the temperature to 199 degrees.  An emergency is declared and the approach is conducted with the left engine at idle.