BMW E36 Blog

BMW E36 Knock Sensors

24th July 2008

BMW E36 Knock Sensors


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…

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posted in Engine, Technical Info, Tips & Tricks, Uncategorized | 18 Comments