Fox tachometer and water thermometer are sometimes absent.

The abnormality of water thermometer is mainly caused by water temperature sensor, thermostat, instrument and related circuits. Judging from your description, the problem is more likely to be the water temperature sensor. Abnormal water temperature signal makes ECU unable to judge the water temperature of the engine at this time. In order to protect the engine, it will enter the fail-safe mode and change the speed.

The so-called water temperature sensing failure protection mode means that when the engine ECU does not receive the water temperature sensing related signal, it will default the water temperature to the normal working temperature (generally about 90℃ by default) for control. If you let go of the throttle and don't refuel, you are idling, but the engine is still running at normal working temperature. This speed will be higher than the normal idle speed, especially when the cold car crashes. At this time, the cooling fans of some models will run at high speed. When you step on the accelerator, signal engines such as throttle position sensor and air flow sensor will further control the operation of the engine. However, since the water temperature is calculated according to the set value instead of the actual value, the ECU will also adjust the mixture concentration according to this signal, and then control the speed.

The engine cooling system has large and small cycles, and the large and small cycle switch is the thermostat. The existence of large and small circulation systems is to ensure the engine temperature. In order to make the engine warm up quickly in a small cycle when it first gets on the bus, when the water temperature reaches the temperature of paraffin in the thermostat (generally around 80℃), it will form a large cycle of heat dissipation to ensure that the working temperature of the engine will not be too high.

When the temperature controller fails, the water temperature meter will change due to unobvious cyclic change or sudden intervention. Generally speaking, its fault performance is often that the pointer of the water thermometer moves back and forth or the water temperature is high and gives an alarm directly.

No matter what the reason is, it is necessary to check and deal with the abnormality of the water temperature meter in time. Because the water temperature signal is incorrect, it will lead to difficult cold start of the engine, high fuel consumption and weak acceleration. I suggest you go to the repair shop for inspection and maintenance as soon as possible!