Whenever one of the controls are used such as the defrost, heat, or AC, the engine constantly revs up. For example, if I am not touching the gas or brake while driving and I use one of the controls, the engine revs up to the point that the vehicle accelerates, just as if I had pressed the gas pedal.
Now the engine computer will raise the engine idle speed automatically to compensate for the additional load of the AC compressor and the electrical load of the blower motor when the AC/Heater controls are operated. This increase should not exceed 250RPM over base idle. If the engine idle does it may indicate a problem with the output voltage of the alternator. You may want to enlist the help of a mechanic, such as one from YourMechanic, to inspect and read out the fault memories in the engine computer to ensure no underlying problems exist.
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