Fluctuations at idle maybe due to plugs, coils, tp sensor. Step by step everything can be checked and verified.
Throttle body service has nothing to do with this.
Throttle body service only clears the surroundings of throttle valve eases and smoothens the throttling and idle is slightly increased like if dirty throttle body was idling the car on 500 so cleaning it will take it to 650-700rpm.
And normal rpm varies between 600-800rpm.