From the Parts Counter — idle speed

The engine that won't die. Cars equipped with carburetors can suffer "dieseling" or "run-on".  This is more common when using unleaded fuel, but can happen with leaded fuel as well.   Dieseling is when after the ignition is shut off (causing the spark plugs stop firing), the engine continues to try to run.  Perhaps you're familiar with the symptom- you turn off the engine and it starts coughing, bucking and clanking, sometimes for up to 30 seconds.   Aside from being embarrassing, repeated occurrences of dieseling can actually damage your engine.   What causes dieseling? When the ignition is turned off, the...