Beginning in 1968 some vehicles may have an idle speed solenoid on the carburetor. All 1972-75 vehicles have idle solenoids. Due to the leaner carburetor settings required for emission control, the engine may have a tendency to diesel or run-on after the ignition is turned off. The carburetor solenoid, energized when the ignition is on, maintains the normal idle speed. When the ignition is turned off, the solenoid is de-energized and permits the throttle valves to fully close, thus preventing run-on. For adjustment of carburetors with idle solenoids see .