Lifan Fengshun 1.0 van runs in the first, second and third gears, and the throttle is unstable. Is it okay to go up and down the fourth and fifth gears?

In this case, you should check the fuel supply and ignition problems of the engine. One is to check whether the oil pressure is normal, and then check whether there is a problem with the nozzle. If there is no problem, check whether the spark plug needs to be replaced, whether there is any problem with the ignition coil and cylinder pipeline, and then check whether the throttle valve is dirty and needs cleaning. All these will affect the idling instability and need the same investigation.