Toyota Repair: 2000 Toyota Celica GTS, coolant temperature sensor, toyota celica gts

Question
2000 Toyota Celica GTS  1.8     2ZZGE Engine  6 Speed Trans  VIN #JTDDY32T0Y0007061   135,000 miles  New spark plugs 10,000 ago  Original plug wires/coils/etc.

Intermittent un-commanded increase in idle speed from approx 700RPM to approx 2000RPM in my daughter's car.  1st happened almost a year ago in wet conditions, no repeat until a couple of days ago.  Happens when the car is warm... Sometimes this an isolated occurrence and sometimes a series of increases and decreases.  No CK engine light, but displays OBD II code of PO300 multiple random misfires (which could be an unrelated old code).  My daughter reports hearing a slight clicking sound during the increase in RPM and the same clicking sound just prior to the decrease back to idle.  All engine operation is normal otherwise.   I did notice that a similar RPM change was reported on a 2001 GTS that you responded to regarding possible air in the cooling system.  Could an internal sensor problem or loose connection on the Engine Coolant Temperature Sensor be causing this problem on our Celica??  I wondered about this to begin with due to the RPM range variance being so close to the cold start RPM in her cycling.  Thanks  

Answer
Unless the coolant was changed or there is a coolant leak there should be no air in the system which would cause this. A malfunctioning air temp sensor would give another code besides the po300, toyota did release a service bulletin regarding the po300 misfire condition, if you would like a copy please contact me at <tedrttr@yahoo.com>