Why does the engine stalls when cold?

Sometimes drivers face the problem of a cold engine that stalls immediately after starting, and this can happen both in the cold and warm seasons. There are various reasons why a cold engine stalls, finding the right cause can be difficult in this situation, so you will need to check properly all the possible causes.

Why do cold engines stall after starting?

There are three main causes why engines stop immediately after the start

  • Problems with the exhaust system
  • The air creation and supply system does not work properly
  • The engine does not receive enough fuel

These three causes can come from various engine parts that are problematic

  • One or more injectors do not hold fuel. As soon as the car is stopped, one of the injectors or more does not have fuel stored because they simply drop it, and at the next car start there is not enough fuel to maintain the engine running when it is cold. In this case is better to check the injectors, especially in diesel engines.
  • Using low-quality fuel. Adding fuel that contains harmful impurities and additives is a sure way to shorten the engine’s life. Because the fuel is bad, during the combustion of the air-fuel mixture, the heat generated is not enough for the engine to develop the required power, and because the engine is cold, it will need extra heat to work in normal parameters until it warms up.
  • A bad or failing throttle position sensor (TPS). When incorrect information about the position of the throttle sensor is sent to the electronic control unit, the ECU can give commands to create a weak fuel mixture, which will lead to the engine stalling a few moments after starting a cold engine.
  • A bad mass airflow (MAF) sensor. If the mass airflow sensor is failing the problems can be as in the case of a bad throttle position sensor, false data will be sent to the ECU, thus, a lean air-fuel mixture will form causing a cold engine to stall after starting.
  • A failing coolant temperature sensor. If this sensor is not working correctly, it will transmit false signals to the electronic control unit (ECU), info like the engine temperature is at its optimum, when in reality, the engine is not warm enough, thus misleading the ECU to give commands to an incorrect air-fuel mixture, which will lead the engine to stop when cold.
  • A bad fuel pressure regulator. The incorrect operation of the fuel pressure regulator will also cause the engine to stop when cold. in colder temperatures, especially in diesel engines, if the fuel pressure regulator is faulty, it may not work properly being helped by summer diesel fuel which is thicker. But as the engine warms up, the operation of the fuel pressure regulator improves. On petrol cars, the problem of the fuel pressure regulator is mostly related to the pressure drop in the system.
  • A failing idle speed control. If the engine is cold, the idle speed sensor has the job to tell the engine to increase its speed (RPM) in order to warm up faster, but because it is not working properly, this sensor may not tell the engine to increase the RPM causing it to simply stop immediately after start.

These are the main things to look at first when you encounter this engine problem. However, there are rare cases where cold engine stalling is caused by something else.

Rare causes of engine stalling when cold

  • Thick engine oil. In winter, as temperature drops, the oil thickens, Therefore, in some cases, after starting the engine, if the driver does not press the accelerator pedal, then until the oil becomes more liquid, it is likely that the cold engine will stall.
  • A faulty fuel pump relay. Especially in petrol engines, if the fuel pump relay is failing, the cold engine might stop.
  • A failing catalytic converter. The cold engine might stall if there are problems with the operation of the catalytic converter. This problem is often caused by the moisture in it which affects the exhaust. However, this is very unlikely to happen because a lot of water is needed to make the catalytic converter not to work at all.
  • Faulty turbocharger.
  • Bad spark plugs. Because the spark plugs are worn, they may give a weak spark, and misfires may occur, followed by an engine shutdown.
  • Lack of vacuum. There may be no vacuum in the intake manifold or vacuum hoses. When starting the cold engine, a proper air-fuel mixture cannot be formed, which leads to the fact that the engine quickly stalls after starting.

What to do when a cold engine stalls?

If you are facing this problem, the first thing to do is to connect an OBD scanner and use it to view the parameters of the engine sensors, as well as read the errors in the ECU.

  • Check for air leaks often caused by damaged hoses, replace those old hoses with new ones. It is also advisable to check the throttle valve, if it is clogged clean it with a special cleaner. For some car owners, the air leak can be stopped by replacing the o-ring on the intake manifold.
  • Use high-quality fuel all the time. Changing the gas station might be a good solution to solve this problem. Just go to a respected gas station that sells high-quality fuel, also it’s best to use the correct fuel according to season.
  • Check the engine sensors. Start by checking the idle speed sensor to see if it’s working properly, then continue the checks with the other sensors mentioned above.
  • Check and clean the injectors. As I said above, injectors may be the reason why the cold engine stalls when starting. It is important to know if the injectors are keeping the fuel off. If they do not hold it, you need to perform additional repairs, such as replacing the nozzles with new ones.
  • Check the spark plugs. In case of significant spark plugs wear or damage, they must be replaced with new ones, especially if they have been there for some time.
  • Check the fuel pressure regulator. The problem with a faulty pressure regulator is solved only by replacing it with a new one.

Conclusion

Finding the cause of why a cold engine stall is a rather difficult and time-consuming task. First of all, you should use an OBD to find errors stored in the ECU to determine where to start. 

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