How do you adjust the idle on a diesel engine semi?

To adjust the idle on a diesel engine semi, locate the idle adjustment screw on the fuel injection pump, which is typically near the throttle linkage. Start the engine and allow it to reach operating temperature. Gradually turn the idle adjustment screw clockwise to increase the idle speed or counterclockwise to decrease it, checking the RPM with a tachometer until the desired idle speed is achieved. Always refer to the manufacturer's specifications for the correct idle RPM range.