What are the reasons for unstable car idling with fluctuating RPM and stalling?
2 Answers
Scooter idling instability with fluctuating RPM and stalling can be caused by reasons such as deteriorated fuel. Below are the specific details: Idling speed too low: Motorcycle engines can generally start at over 200 RPM, but may stall due to excessively low idling speed that cannot be maintained. Deteriorated fuel: It is possible that the fuel in the carburetor has deteriorated, leading to poor combustion which causes unstable idling and difficulty starting. Draining some fuel through the drain pipe at the bottom of the carburetor usually solves the problem. Nozzle issues: Air bubbles blocking the nozzle can cause unstable engine RPM and stalling. Additionally, using excessively dirty fuel may clog the nozzle, or leaks in the fuel pump and fuel lines can result in abnormal fuel pressure, causing unstable idling.
Recently, my car's idle speed has been unstable, fluctuating up and down and frequently stalling, which is really worrying when driving. From experience, it's likely that the throttle body is too dirty with excessive carbon buildup, causing the idle speed control valve to get stuck and resulting in unstable RPM. Alternatively, there might be an air intake pipe leak, such as aging rubber tubes with cracks, allowing external air to sneak in and disrupt the air-fuel mixture ratio. Another possibility is an underperforming fuel system—for instance, clogged fuel injectors causing poor fuel supply or insufficient fuel pump pressure leading to intermittent engine operation. Ignition components could also be faulty, like worn-out spark plugs or faulty coils causing stalling. Lastly, sensor malfunctions, such as inaccurate readings from the mass airflow sensor misleading the ECU, could be the culprit. Don't delay—this situation is extremely dangerous. Get it checked and repaired at a professional shop as soon as possible. Cleaning the throttle body and checking for leaks can usually resolve the issue. Also, remember to regularly replace the air filter during maintenance to prevent carbon buildup and avoid further trouble.
