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Rough Idle refers to the condition of a vibrating and shaking engine when pressing the gas pedal. The most common possible causes of this trouble come from an incorrect idle adjustment, PCV (Positive Crankcase Ventilation), or EGR (exhaust gas recirculation) are stuck open and defective fuel injectors. 

  • If the engine starts and then stalls, it may happen before or after the engine warms up, after idling or slow speed driving, or even after a full load or high-speed driving, Stalling can be also caused by a sticking PCV (Positive Crankcase Ventilation) or improper adjustment of the carburetor idle solenoid.
  • If the engine stalls before warming up, this could be also due to dirt or water in the fuel line or filter, a defective fuel pump, or a plugged fuel tank cap. In the carburetor, a low float setting, clogged idle system or carburetor icing could cause stalling. Some ignition troubles can cause stalling ignition troubles that cause stalling often prevent starting. On contact point systems, the burned points and an open primary resistor can cause stalling. During cranking the resistor is bypassed, after the engine starts, the current must flow through the resistor, If the resistor is  open the engine will stall as the ignition key returns to run
  • Sometimes a carburetor chole valve may stick closed, The mixture will then be too rich for a hot engine so the engine stalls
  • If the manifold heat control valve sticks close the air fuel mixture will be too hot and too lean, causing stalling. A low idle speed setting can cause stalling as the engine warms up. If the door in the thermostatic air cleaner sticks closed, the air fuel mixture will overheat and be too lean and will cause engine rough idling