What are the reasons for unstable idle speed and stalling in natural gas vehicles?
2 Answers
The reasons for unstable idle speed and stalling in natural gas vehicles are as follows: 1. Severe engine carbon deposits: When there is excessive carbon buildup inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, resulting in an excessively lean mixture during cold starts and making it difficult to start. Under these conditions, the engine will only start easily once the carbon deposits have absorbed enough gasoline to become saturated. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction, making the mixture too rich. This fluctuation between lean and rich mixtures causes idle speed fluctuations after a cold start. 2. Excessive carbon deposits and dirt in the throttle body and intake tract: Too much carbon buildup and dirt in the throttle body and surrounding intake tracts change the cross-sectional area of the air passage, preventing the control unit from precisely regulating the idle air intake. This leads to an overly rich or lean mixture, resulting in abnormal combustion.
I've worked in repair shops for years and seen many natural gas vehicles with unstable idling or stalling issues, mainly due to incorrect air-fuel mixture ratios. Possible causes include improperly adjusted pressure regulators or gas leaks leading to insufficient fuel supply, causing unstable airflow at idle. Carbon buildup jamming the idle control valve can also disrupt the air-fuel ratio. Worn-out spark plugs with weak ignition may cause stalling, especially during startup or low-speed driving. Contaminated oxygen sensors sending false signals can mislead the ECU into incorrect fuel delivery, worsening the problem. Other unexpected causes include clogged filters or vacuum system leaks affecting pressure. Regular checks of the pressure regulator and cleaning the idle control valve can prevent many issues. Don't underestimate maintenance - delayed repairs may cause greater engine damage, and roadside diagnostics can be dangerous. I recommend visiting professional repair shops with diagnostic tools rather than DIY attempts to avoid safety risks.
