BMW E36 Blog

Hi all,

As you may know, I’m still having a problem with my car’s idle. I mainly have 2 problems:

1. When I start my car, the idle bounces for a while and then it becomes stable.

2. While driving, I sometimes notice that the RPM (Rotation Per Minute) moves down until it reaches 200 or maybe less then it comes back again especially when I’m pressing the clutch pedal.

After running an extensive research about these problems, I’ve found many solutions or you may call them suggestions and they’re all over the forums. The solutions for a perfect idle in a BMW E36 are:

1. Cleaning ICV (Idle Control Valve): A very straight forward task. This unfortunately didn’t solve my problem completely but it helped a little bit.

2. Checking/Replacing the TPS (Throttle Position Sensor): I tried to replace it, but nothing has changed.

3. Check for vacuum leaks: Just buy a carborator cleaner can and while the engine is running, spray it around the engine and make sure to listen to the engine sound and see if you can detect any change in the engine’s idle. If anything has changed, it means that you have a vacuum leak. This didn’t result in any problems in my case.

4. Check the ignition coils: I didn’t find any problems with this either.

With these options out of my way, I’m left with a knock sensor error code when I check my car for problems. Actually it’s the 2nd knock sensor which is located in the left side of the cylinder block. For those who don’t know what a knock sensor is, it’s a sensor used to monitor the combustion chamber for engine-damaging knock (according the the Bentley Manual). Unfortunately, the second knock sensor requires removing the upper section of the intake manifold to replace it. So, as you can see, it’s not a very straight forward task, so I took the car to a mechanic and he replaced it (I suggest you do the same if you have the same problem). Now, the knock sensor is working properly. I also asked him about the DISA valve and it turned out that I had a vacuum leak that prevented it from working properly.

Now, after I fixed both problems, I got rid of the second problem completely. Now, I need to do more research about the first problem. I know it’s not going to be that simple and I will need to dig deeper before I have my perfect idle. But I’m not going to despair…

BMW E36 Blog: The ultimate BMW E36 information source.

Rough idle problems are really common on BMW E36 cars and there are a lot of problems that may cause this to appear. First I will show you a video of such a rough idle and then list the possible problems that may cause that.

Take a look:-

The possible reasons for such a problem are:

1. Oxygen Sensor is gone: You can run a diagnosis to see if this is the problem. If you find out that it’s the problem, you should replace it. Read Everything you need to know about Oxygen Sensor! for more information about oxygen sensors.

2. Idle Control Valve: Dirty idle control valve is a very common problem in BMW E36 cars that may cause rough idle. You can use this DIY (Do It Yourself) to learn about Cleaning E36 ICV (Idle Control Valve)

3. Plugs and Distributor: You may need to replace these to solve your problem. I however don’t have a way to check them before replacement.

4. The Throttle Position Sensor (TBS) and/or connections may be bad: You can simply disconnect it and see if your problem is solved or not.

BMW E36 Blog: The Ultimate E36 Information Source.