What about intermittent automobile exhaust?

As no existing vehicles are seen, the analysis shows that the main fault causes should be carbon deposition in throttle and air intake. When the vehicle is in a cold state, part of the gasoline is adsorbed, which will lead to the lean mixture when the engine is idling, which will lead to the unstable idling of the cold car. So you should check whether there is too much carbon in the throttle and air intake. If there is too much carbon deposit, the cross-sectional area of the air passage will change, which will make the control unit unable to accurately control the idle intake, resulting in too lean mixture, abnormal combustion and unstable engine idle speed. You can make a field trip based on the above analysis.