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. There is a good chance the IAC valve needs to be cleaned/changed. How many miles on the car?
Edit. IAC valve how to in UIM/LIM rebuild with pics in
Duratec Maintenance FAQ
And to confirm if it is not the a/c compressor or pulley, does it happen when the heat is on and the switch is turned to Panel or Floor. Note that with the heat on, and switch turned to FLR/DEF or DEF, the A/C also comes on to help dehumidify the interior.