Those nuts are not used to set the idle speed. They are used to remove the excessive slack in the cable so the cruise control will respond accurately and hold the right speed. If you try to use them to control idle speed, it can surge when the engine rocks and tugs on the cable. There must be a little slack in the cables.
There is no idle speed adjustment on computer-controlled engines. The idle speed motor is pulsed to various positions by the Engine Computer to set the desired idle speed. As the motor slowly rotates, it turns a threaded rod with a valve on the end. That valve exposes more or less of an air bypass passage around the throttle blade. At the same time, the computer adjusts the amount of fuel spraying into the engine.
On those few engines that still have an idle speed screw, that simply sets the starting point, then the computer continues to make the changes it wants by running the idle speed motor. If the idle speed screw is used to increase idle speed, the computer will just close the idle speed motor and valve to bring the speed back down.
Apr 26, 2017 at 7:12 AM
