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BMW E36 Knock Sensors

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24th July 2008

BMW E36 Knock Sensors

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


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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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This entry was posted on Thursday, July 24th, 2008 at 4:56 pm and is filed under Engine, Technical Info, Tips & Tricks, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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There are currently 9 responses to “BMW E36 Knock Sensors”

Why not let us know what you think by adding your own comment! Your opinion is as valid as anyone elses, so come on... let us know what you think.

  1. 1 On July 24th, 2008, Johnny said:

    Hi Tony!

    If you could provide me with your email, I would send you the photos of my car, I promised to send nearly a month ago :p

    Take care,
    Johnny

    posted on July 24th, 2008 at 7:25 pm

  2. 2 On July 25th, 2008, Guetzer said:

    Hey, I had the same problem with my car, turned out to be the camshaft sensor. :)
    good luck!

    posted on July 25th, 2008 at 10:00 am

  3. 3 On July 25th, 2008, Tony Sticks said:

    @Guetzer: You know something you may be right. My camshaft sensor is stripped out. But it’s doesn’t throw an error when I run the diagnosis. Did your camshaft sensor throw an error when you had that problem?

    posted on July 25th, 2008 at 11:47 am

  4. 4 On July 25th, 2008, Tony Sticks said:

    @Johnny: My email address is tonysticks *AT* bmwe36blog *DOT* com

    posted on July 25th, 2008 at 11:50 am

  5. 5 On July 26th, 2008, Guetzer said:

    Yeah, my camshaft sensor gave an error on the diagnosis.

    posted on July 26th, 2008 at 2:26 pm

  6. 6 On July 26th, 2008, Tony Sticks said:

    @Guetzer: Mine doesn’t. I will try to replace it and see if that helps…. thanks anyway for the help.

    posted on July 26th, 2008 at 10:24 pm

  7. 7 On July 27th, 2008, Guetzer said:

    Sure man! no problem :) hope it works!

    posted on July 27th, 2008 at 1:52 pm

  8. 8 On October 3rd, 2008, Libour said:

    Hi everyone,
    I have got the same trouble with my e36 318iS. But there is no error which is related to knock sensors in diagnostic. sometime there is only error of vacuum leak and lambda sensor. My mechanist has tried to replace both - all the intake manifold and lambda sensor. It was still the same. He doesn’t belive me it could relate with the knock sensor. What do you think about? Tony, have you already got rid your problem completly of? If you have, what was the problem? thank you for any comments! Libour

    posted on October 3rd, 2008 at 2:14 pm

  9. 9 On October 6th, 2008, Tony Sticks said:

    @Libour: Honestly, replacing the knock sensor didn’t solve the problem completely but it definitely enhanced the idle. From your description, you say that you’re getting errors for lambda sensor and vacuum leaks. So, I suggest you keep looking there. I also suggest checking the TPS (Throttle Position Sensor) and Cleaning your BMW E36 ICV (Idle Control Valve). Replacing the knock sensor(s) is NOT an easy task and you should be 100% sure it’s not working before replacing it.

    posted on October 6th, 2008 at 9:55 am

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