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.
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 at idle is a problem that I have witnessed and had to fix numerous times over the years.
There are a lot of potential things that can be causing your BMW to shake. There are even more if we do not consider when exactly your BMW is shaking. If your BMW was shaking when you hit the brakes or perhaps your steering wheel was the main component shaking, this would narrow the possible causes in a different direction.
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
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 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:
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.
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.