The Secondary Throttle Plate (STP) map controls how much the secondary throttle plates open, relative to primary throttle position and RPM. The value in the map is the amount the STP is open.  The map value is selected based on Throttle Position Sensor (TPS, top axis) and RPM (side axis).

In the example below the highlighted blue cell shows that the Electronic Throttle Valve will be 59.6% open when the engine is running at 5600RPM, and the Throttle Position Sensor is at 60%. 

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