Most of us encountered such a problem in the driving process, the car engine shakes while idling, and idling speed up to 950 RPM, then we got into the panic. Generally, it is not a big issue, we just need to figure out what causes lead to this symptom. In fact, there are several reasons for this symptom, roughly divided into three main reasons: engine misfire, excessive carbon deposition in throttle, excessive pressure fluctuation of fuel system.

First of all, let’s figure out what’s the misfire.

The cylinder is a combustion chamber in the engine, in which a piston is driven by the pressure or expansion force due to the combustion of the mixture. This symptom is caused by carbon deposit of the spark plug, leading to a cylinder ignition coil failure, when the engine is work at idle, only a few cylinder are reciprocating alternately up and down, so it will cause the engine vibration.

In general, the engine idling is caused by the misfire, and will affect the idling condition of the vehicle. At this time, if the vehicle is accelerating and the engine is insufficient power, resulting in engine idling.

Carbon deposit of the throttle valve

The throttle is closed and the idle bypass valve is opened when at idle. However, if the throttle is seriously carbonized and the gas flow of the idle bypass valve is poor, the air intake of the engine through the idle bypass valve will be uneven, thus leading to the increase or decrease of the engine speed.

If there is too much air intake, the engine idling speed will certainly rise, and due to carbon deposit, the most possibility is unstable idle speed.

In general, the symptom caused by engine carbon deposit is easy to distinguish, the vehicle fuel economy increases, the vehicle power performance decreases. If both of these conditions are good, but you still engine idles, then you need to check fuel system.

The pressure of the fuel system fluctuates greatly, and the fuel injection quantity is not uneven, which directly leads to the poor atomization effect of the engine fuel injection quantity, and the fuel injection quantity of each cylinder is not even,  also easily leads to the increase of engine speed and unstable idling.

However, engine is shaking while idling, and the idling speed is too high, most of the reason is due to misfire. You can check the cause of misfire in detail, and then check the cause of the problem.