BMW’s are excellent cars, and for the most part they run pretty well. But that being said, any vehicle is going to have a problem and need some maintenance from time to time. One common problem that you may experience is a BMW that shakes at idle.
A BMW shaking at idle could have several causes. Bad motor mounts is one of the most common culprits in older higher mileage vehicles. Other common causes of a shaking idle include bad fuel injectors, spark plugs and a vacuum leak. Performing a basic diagnosis of your BMW shaking at idle problem is relatively easy.
Let’s take a look at the different causes of a BMW shaking at idle. Let’s also take a deeper dive into how we can diagnose and identify what is causing your BMW to shake at idle.
If your BMW is vibrating when accelerating, check out this article here as well.
BMW Shaking At Idle Overview
Nobody likes to have problems with their vehicles, especially something as expensive to purchase and maintain as a BMW. But BMWs have issues to and shaking while idling is a problem that I have witnessed and had to fix numerous times over the years.
There are a lot of potential issues that can be causing your BMW to shake. There is an even greater potential list of issues if we don’t consider the circumstances of your shaking vehicle (at idle, while driving at certain speeds, etc.). If your BMW shakes when you hit the brakes or you notice that your steering wheel shakes as well, this will narrow down the range of possibilities.
Luckily, we already know that your BMW’s problem is that it is shaking at idle. Therefore, we can focus on some problems that most commonly cause this symptom.
I also want to remind you that all idling engines shake at least a little bit. Some engines shake far more than others, but it is important to remember that it is completely normal for your BMW’s engine to shake a little bit. Watch this video here to hear what a shaking BMW engine sounds like.
What is Causing Your BMW to Shake at Idle?
First thing’s first: Check the codes
There are a lot of potential problems that could be causing your BMW to shake while idling, so we want to narrow down the list as much as possible. You might be surprised to learn the sheer amount of issues that your BMW’s computer can identify and register in the vehicle. No one wants to see that “Check Engine” light on the dashboard, however, it is extremely useful in narrowing down potential issues. If you don’t have a code reader yet, one excellent option is the Foxwell.
If your check engine light does not narrow down the problem, here are some extremely common causes of shaking at idle:
Bad engine mounts
Engine mounts play an extremely important role in your vehicle by keeping engine movement to a minimal. They are bolted from the frame to the engine block. There are a number of symptoms you might experience if your engine mounts fail but by far the most common is an excessive amount of shaking in idle. In fact, a blown engine mount can cause vibration throughout the passenger area and can even cause your engine to essentially bounce when you hit bumps in the road.
How to identify a blown engine mount
Diagnosing a blown engine mount is a relatively straight-forward process. The most common indicators of a blown engine mount are that the vehicle is higher mileage (100k+) and lots of engine movement. But a fast way to identify the problem is to open the hood while your BMW is at idle and put your foot down on the accelerator while someone watches the engine. If there is a significant amount of engine movement when you press the accelerator, then you have bad engine mounts.
Luckily engine mounts are not very expensive and the labor to replace them is relatively low.
Bad fuel injectors
Bad fuel injectors will cause a host of problems in your BMW, not the least of which is a shaking idle. The fuel injector delivers gasoline from your fuel tank into the intake manifold. Unfortunately, over time fuel injectors can get clogged with carbon or they can have an electrical fault. A single faulty fuel injector can throw off the air-fuel ratio in your engine’s combustion chamber.
How to identify a bad fuel injector
A faulty fuel injector will let you know that it has failed, they do not hide the ball. Some common symptoms include check engine lights, shaking at idle, misfiring or your car may not even start.
There is a tool that you can use called a fuel pressure tester which will help you identify whether the fuel injectors are faulty. You can rent one at your local auto parts store. If you do not feel comfortable working with your BMW’s fuel system then I strongly suggest that you have a certified mechanic fix this problem.
Vacuum leaks
Vacuum leaks are never a good time and they are even worse when they cause your BMW to shake. A vacuum leak essentially just means that air has bypassed the typical intake path. There are a number of vacuum hoses carrying air that attach to your engine and if one of them cracks or loosens it can cause a vacuum leak. Vacuum leaks cause a lean fuel-air mixture and will often create a shaky idle and an erratic RPM gauge.
How to identify a vacuum leak
Finding a vacuum leak can be really straightforward or extremely time-consuming. The most notorious cause of BMW vacuum leaks BY FAR is the rubber intake boot that connects the Mass Intake Sensor to your Throttle Body.
Here is a picture of the intake boot:
This boot is infamous for cracking overtime and can cause loud and obvious vacuum leaks.
Other common sources of vacuum leaks include the brake booster hose, throttle body gasket, and intake manifold gasket. There are other potential sources of vacuum leaks on your BMW, but these are certainly some of the most common.
In order to find a non-obvious vacuum leak you will likely need a tool called a smoke machine. These tools typically cost upwards of $100 and they basically pump smoke into your vacuum lines so you can identify where the smoke escapes. You can pick up a good quality one here, alternatively, I have seen others build their own smoke machines and Scotty Kilmer even used a cigar here.
Other causes of shaking while idling
We have just discussed a few of the most common causes of shaking at idle, however, you should be aware that there are more common issues. To name a few: (i) worn out ignition system components, (ii) MAF Sensor and (iii) clogged/bad fuel injectors.
Ignition system issues
A worn out spark plug or ignition coil will very quickly cause an engine shaking issue along with additional symptoms such as: (i) misfiring, (ii) difficulty starting and a (iii) reduction in power.
Ignition system issues will usually show up in your check engine codes. To confirm you have a bad ignition coil, you can swap out the coil with a cylinder that is not throwing a check engine code. If the code reads to the changed cylinder, then you know you have a bad ignition coil.
Ignition components are very quick and easy to replace on the vast majority of BMWs, always change all of the spark plugs at once, but the ignition coils can be changed individually.
You can read more on BMW spark plugs here.
Faulty MAF Sensor
MAF (Mass Air Flow) Sensors are extremely easy components to replace and they also serve an incredibly important role. Your MAF Sensor is responsible for measuring the amount of air entering the intake manifold. The vehicle then uses this information to determine how much fuel the engine needs for a correct fuel-air ratio.
When the MAF Sensor fails, your vehicle will idle extremely roughly and may not even start.
The good news, is that oftentimes the MAF Sensor is just dirty. Most autoparts stores sell MAF Sensor cleaner which you can use to clean any built-up gunk on your sensor. You can check out a video here on the process.
Faulty fuel injectors
Faulty fuel injectors are another potential cause of shaking at idle. BMW fuel injectors are quite reliable, however, they still have a lifecycle like any other part. In my experience, I typically start replacing fuel injectors at around 80,000 miles.
There are a number of symptoms to faulty fuel injectors, including: (i) noticeably declining fuel mileage, (ii) misfiring, (iii) engine performance declines and (iv) a very rough idle.
One great way and easy method to try and resolve a fuel injector issue is to pump the injectors with fuel injector cleaner. The fuel injectors have tiny holes where the fuel shoots out and even very fine particles can clog these injector holes. Your fuel filter is designed to filter out the vast majority of these particles, however, some particles still slip through overtime.
You can check out a DIY video on fuel injector cleaner here.
Conclusion
In this article we discussed what a BMW shaking at idle actually sounds like and when it is a problem. We also discussed that there are several different potential causes of a BMW shaking at idle and some are much more common than others.
Finally, we identified the easiest ways to diagnose what is causing your BMW to shake and when it might be time to call a professional.
Sources
https://www.torque.com.sg/advice/vacuum-leak-what-causes-it-and-expensive.
E36 Engine Mount Replacement Step-by-Step Guide, Tools, and Parts (eeuroparts.com)