A situation in which the idle speed spontaneously and periodically begins to change for no apparent reason or any action by the driver is called floating idle speed. In some cases, it comes to the fact that the engine stalls.
Most often, this occurs in engines with electronic fuel injection and is associated with air leaks. The computer control unit for injection engines calculates the volume of air entering the cylinders and, taking into account information received from various sensors, controls the solenoid valves of the injectors. When air is leaking, the throttle position sensor diagnoses excess air, and the temperature sensor signals the need to reduce the flow of fuel. The computer, receiving such conflicting information, begins to decrease and then increase the idle speed. Automatic regulation of the power system is violated. On engines with a carburetor power system, floating speed occurs when the servo motor or the throttle thrust is incorrectly adjusted. This malfunction occurs only in cases where, when adjusting the carburetor, you do not start the adjustment with the idle speed adjustment screw or the throttle stop screw, but turn all the screws in a row a little at a time. And if the engine does not react in any way, forget to return them to their original position. As a result of such unskilled interventions, there appear dips during a set of revolutions, floating idle speed, increased fuel consumption and other negative effects. On diesel engines, not only idle speed can float, but also revolutions in the region of 1000-1500 rpm. The only reason for this is the sticking of the movable blades in the fuel pump. This only happens if they are rusted. And rust can appear only due to the presence of water in diesel fuel. As a rule, it is found after a long parking of the car. Experienced drivers, before leaving their diesel car for a long time, pour a liter of engine oil into the fuel tank and drive on this fuel for the last day. Diesel, of course, smokes, but all parts of the fuel pump are covered with a thin protective oil film. In addition, floating speed can be the result of the following reasons: improper operation of the ignition system, incorrect operation of the flow meter or lambda probe, air flow sensors, coolant temperature, air temperature. As well as changing the settings of the ECU, contamination of the nozzles or low-quality gasoline.
