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Idle Problems in the BMW 318i

A Guide to Idle Problems in the BMW 318i

Have you ever noticed that your car is vibrating heavily while standing still at a traffic light? Or maybe your car suddenly stopped while the engine was running at a standstill condition? Don’t worry, you are not the only one. Idling problems are common in every type of car, even luxury ones. Thus, today we are going to discuss the idle problems seen in a BMW 318i.

Generally, two types of idle problems occur in a BMW 318i – stuck in high idle and stalls in low idle. The former is when the engine is revving at higher speeds than normal even when you are not asking it to move. While the latter is when the engine just stops or stalls when you put the car in neutral and wait.

High idling is caused generally due to excess fuel reaching the engine or if there is a thermostat problem. On the other hand, engine stalling can be caused due to a variety of reasons like blocked filters, or even vacuum leaks. We will explore all these problems in detail in this post. So, stick around to find some solutions.

What is Idling?

idling rpms
Typical Idling RPMs | Image Credits: Unsplash

Before diving deep into the problems, first a little background on what idling is. As you might know, internal combustion engines cannot deliver power at 0 RPM, unlike electric cars. The engine needs to move with a certain amount of force to overcome the frictional forces within the whole system and keep the combustion process going.

The speed at which it achieves this minimum torque is known as the idling RPM. You generally feel this speed when the car is put to neutral gear and the engine is left on. Since this is the lowest speed that the engine functions at, it is sort of extreme and thus a fragile operating point. Therefore, several problems can occur at this point as you will soon discover in this post.  

High Idling

As mentioned before, high idling is basically when the car is revving at neutral gear a bit higher than normal. What you may not know is that this is rather intentional for most cars in certain conditions. This generally happens initially when the car is started in especially cold conditions. The engine needs to warm up to the correct temperatures first. This allows the engine to work efficiently.

Thus, to reach this point fast, the engine deliberately idles at a higher RPM. However, the real problem is when the engine doesn’t go back down to the correct idling speed even after a few minutes of warming up. This may happen due to the following reasons.

Stuck Thermostat

The thermostat in a car
The thermostat in a car | Image Credits: Youtube – Top 5 Auto Repairs

One possible reason the engine doesn’t return to normal idling is that the thermostat in the cooling system is stuck in the open position. In such a state, the coolant keeps flowing through the engine which doesn’t allow the engine to heat up fast enough. It keeps the engine at a lower temperature even when not required. Fortunately, the solution isn’t too hard. All you need to do is change the thermostat of your engine. This should generally resolve the problem.

MAF Sensor Malfunctioning

Another possible problem of high idling is if the engine is being supplied more fuel than necessary. Thus, if you are confident that the weather wasn’t playing a role in your idling problems, you may want to investigate this instead. This problem is generally caused by a MAF (Mass Air Flow) sensor. This sensor is responsible for measuring the amount of air that is being supplied to the engine. Accordingly, it asks the fuel injector to inject the right amount of fuel.

Hence, if for some reason, the MAF malfunctions, it records that extra air is being sent to the engine. Thus, extra fuel is sent to the engine which causes it to rev higher than normal. To solve this problem you can try to clean the MAF sensor once after taking it out. However, if the problem persists, you may want to replace the sensor entirely.

Hunting or Knocking

bad sparkplugs
Bad Sparkplugs can cause knocking or Hunting | Image Credits: Pixabay

There is one more type of idling that you may face which is known as hunting sometimes. In short, it is a very violent form of idling that occurs occasionally. It is generally caused by a phenomenon known as knocking. Without going too deep into it, just know that it is bad for your engine and may lead to damage.

This phenomenon generally occurs at lower RPMs and the cause is usually the sparkplugs, ignition coils, or the engine calibration. When the spark plugs or ignition coils aren’t working properly, you get improper combustion. Such combustion leads to the hard vibration that you feel. If these components are the problem, simply replacing them should do the trick.

On the other hand, if the ECU is the cause of the problem, it might be a bit trickier to solve. Switching the car on and off or disconnecting the battery temporarily might help reset the ECU. But if none of these tricks works, you might want to take the car to the closest dealership. They will thoroughly troubleshoot it and identify the root cause of the BMW 318i idle problems.

Low Idling or Stalling

As you have seen, Idling is the lowest RPM required for the engine to sustain the operation. However, sometimes, due to various reasons, the engine drops below this speed. Since the operation is no longer sustainable below this speed, the engine stops running. Such problems are generally caused due to a loss of power. This loss of power can be caused by either a lack of fuel or a lack of air being supplied to the engine.

Lack of Air

throttle body
Cleaning a Throttle Body | Image Credits: Youtube – Scotty Kilmer

First, let’s talk about the lack of air. There may be two primary reasons that the air being supplied to the engine is running low – a blocked air filter or a blocked throttle valve.

Air filters often get blocked due to the accumulation of dirt over time. Hence, they are often changed during the mandatory service sessions. If they get blocked, naturally enough air can’t get through and the engine can’t function at lower speeds anymore. Simply replacing the filter or cleaning it should resolve the problem in this case.

The other problem is that the throttle valve doesn’t open as much as required during idling. This valve controls the amount of air that flows to the engine. However, over time, due to carbon deposits or other particles, this valve might get blocked, and the operation may be sub-optimal. This lack of air causes the car to stall as the air-fuel mixture can’t combust anymore. To solve this, you can take out the throttle valve and try to clean it. But you should be careful not to damage it. Otherwise, you can even replace the throttle valve to fix the problem.

Vacuum Leaks

One cause that might also lead to the stalling of your car is the possibility of vacuum leaks in the system. As you might know, the engine causes a partial vacuum during the intake stroke to suck air inside. However, if there are any leakages, this suction pressure reduces, and thus not enough air can get in time.

These leaks are generally caused by gaskets or bolts that haven’t been placed/tightened properly. To fix this issue, you will have to first check where the location of the leak is. Once determined, you can check if the torquing of the bolts are right or not in that component. If they are, you might have a problem with the gasket which needs to be replaced.  

Lack of Fuel

fuel levels
Fuel Problems | Image Credits: Pixabay

The next source of the problem might be the lack of fuel. This problem can be caused by the fuel filter being blocked just like the air filter. While this is rarer, it is certainly possible. In such cases, it is best to replace the fuel filter altogether.

Alternatively, it might be the problem of the MAF sensor again which is sensing the wrong amount of airflow in the engine. Accordingly, a lower amount of fuel is combusted which cannot provide the power to run the engine at the idling speed. Luckily, the fix is the same and equally easy – just replace the MAF sensor!

Sensor Issues

Finally, if it is neither of the above, then you might have a problem with the cam or the crank position sensors. These sensors identify the position and speed of the piston and accordingly determine the right time to inject the fuel and ignite it.

If these sensors are not working properly, the timing will be off. Such timing delays (or advances) can also cause power losses leading to idle problems in your BMW 318i. Like the previous problems, the solution here is to replace the malfunctioning sensors. Hopefully, this resolves your problems.

Final Thoughts

Idle problems in your BMW 318i can be a huge bother while driving especially if stop at a stop sign only to find out your engine has mysteriously stopped. It becomes exceedingly annoying to drive a car. That is why we hope that you have found the solution to your problem in this post.

If you intend to try out these solutions, peek into the owner’s manual to help you better understand the car. Since you will be dealing with the cooling system or the battery system of the car, remember to take the necessary safety measures.

Alternatively, you can always take the car to the nearest dealership. We recommend that especially if none of these solutions checks out. Either way, we hope that your engine never stalls again and always idles at the right speed!


Abheek is an Engineering student with a background in Automotive Engineering and Sustainable Energy Engineering. He has worked in Engine Development for a couple of years but is quite interested in Electric Vehicles too! In his free time, he likes to use his knowledge to help others with their car problems. Other times, he can be found following the sport of Formula 1.

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