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Thread: Temp Sensors, What are they all?

  1. #1
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    Temp Sensors, What are they all?

    I have a 1986 325e automatic that I am having a "rhythmic" RPM issue with while the car is warm and under power. The RPM issue doesn't appear first thing when the motor is ice cold, but starts once the motor is warm, IE, the thermostat opens. Additionally, I just changed the plugs and the old ones were black from what I assume is a rich fuel mixture.

    My question is, which sensor is linked to RPM and or fuel mixture? I assume one of the sensors is dedicated to the temperature gauge? I looked on Real OEM and am still confused what the names are, their function and part numbers.

    RED: Function? Part Number?

    YELLOW: Function? Part Number?

    BLUE: Function? Part Number?

    GREEN: Function? Part Number?
    Attached Images Attached Images
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  2. #2
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    No e30s, again :(
    The blee one goes to the ecu to tell it engine temp, if i remember right. You should have one with a single pole in it, that goes to the temp gage. The other two, i cannot remember but i guess i will have to google it again as both of the eta at my house now have that hunting idle

  3. #3
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    It's frustrating to say the least. Others have mentioned the issue could be a bad AFM, but the one in the car is a fresh rebuilt unit. I am thinking something temp sensor wise considering it seems to only start acting up once the thermostat opens and the sensor is hit by warm coolant.
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  4. #4
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    No e30s, again :(
    I noticed before i had to replace the head on one of these that one had a hunting idle and one did not but i could get the one to hunt if i took the oil filler cap off and put it back when it was running, introducing a vacuum leak. I think that since the car is running on a start up map, and not the o2 sensor, when warming up that its vacuum related. Once i reaches a certain temp than it starys going off o2 readings and since the vacuum leak is making it read off, that is what is causing my problems

  5. #5
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    89 325i track, 91 318is

  6. #6
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    From what I understand of these sensors:

    Red: Thermo Time Switch - control start valve - closed below 32F
    Yellow: Coolant Temp Switch for idle control - closed above 113F
    Blue: Coolant Temp sensor for temp gauge and service interval
    Green: Coolant Temp sensor for ECU

    Why so many? Good question for the BMW Engineers.

    I've been trying to pin down my idle issue. Cold and heat soaked after sitting, idles great. In between, about 1K. Have replaced all the sensors but the Thermo Time due to its cost.

    Good luck and update the thread when you get it sorted.
    2004 525i Sport, Manual - 1985 325E Coupe Manual

  7. #7
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    So, would the opinion be that having the motor smoke tested for any vacuum leaks would be a good investment? I think I have read that even a small leak around the intake manifold to head mating surface will cause issues. I've replaced as many of the hoses as I can find.
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  8. #8
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    Can these be tested?
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  9. #9
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    No e30s, again :(
    I have never done one but any car can be tested

  10. #10
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    Quote Originally Posted by 1SGDHORN View Post
    Can these be tested?
    I don't want to be a smart a$$, but of course! As you are finding out, idle issues are probably the most discussed single item across the forums.

    First, get yourself a Bentley manual as that is the bible of trouble shooting. There are tests for each sensor, the Idle Control Valve (ICV) along with the Idle Control Module (ICM). Besides the temperature sensors, ICV and ICM, you have the throttle position sensor and air flow sensors which all effect idle.

    Probably the best summary I have found is: http://www.verrill.com/car/e30_idlefaq.shtml

    Be patient, sorting this out can be VERY frustrating!
    2004 525i Sport, Manual - 1985 325E Coupe Manual

  11. #11
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    Thanks tomstin. Does it matter that my car idles perfectly smooth? The "hunting" only happens under power and only when warm. My ICV is new as is the AFM. Not that I like to just through parts at the car, but the sensors are cheap enough to replace, well except for the one. I think I will see how new sensors work.
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  12. #12
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    No e30s, again :(
    Let us know how it goes. I unplugged all of mine and replugged them in, while checking for a possible ground issue for the temp gage and now my hunting idle is gone

  13. #13
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    What do I do when one of the sensors in no longer available? And the top is loose/fell off. I epoxied it back on, but would like to find a new one. Anyone know where these can be purchased?
    Attached Images Attached Images
    "Life is too Short to drive boring cars"


    1986 325E
    1989 325iX (Long term 5-speed/refresh project)
    1993 MB 300E
    1995 MB E320
    2000 Audi TT (Winter AWD snow beast)
    2007 Porsche Cayman S (Summer car)
    2009 VW Touareg

  14. #14
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    No e30s, again :(
    Uh oh, nla means eta powered cars, 3 and 5 series are going to be dropping off the road soon
    No e30s again.

  15. #15
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    Quote Originally Posted by 1SGDHORN View Post
    What do I do when one of the sensors in no longer available? And the top is loose/fell off. I epoxied it back on, but would like to find a new one. Anyone know where these can be purchased?
    https://www.getbmwparts.com/oem-part...ch-12631279722

    Good luck! If they say they don't have it, might call a BMW dealer directly - they can check inventory nationwide and get it from another dealer that has new-old-stock.

  16. #16
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    Quote Originally Posted by 1SGDHORN View Post
    What do I do when one of the sensors in no longer available? And the top is loose/fell off. I epoxied it back on, but would like to find a new one. Anyone know where these can be purchased?
    How about here:
    http://stores.ebay.com/EuroMotive-Restorations/_i.html?_nkw=coolant+sensor&submit=Search&_sid=644 90547


    2004 525i Sport, Manual - 1985 325E Coupe Manual

  17. #17
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    Quote Originally Posted by tomstin View Post
    From what I understand of these sensors:

    Red: Thermo Time Switch - control start valve - closed below 32F
    Yellow: Coolant Temp Switch for idle control - closed above 113F
    Blue: Coolant Temp sensor for temp gauge and service interval
    Green: Coolant Temp sensor for ECU

    Why so many? Good question for the BMW Engineers.

    I've been trying to pin down my idle issue. Cold and heat soaked after sitting, idles great. In between, about 1K. Have replaced all the sensors but the Thermo Time due to its cost.

    Good luck and update the thread when you get it sorted.
    Motronic 1.1, 1.3 and 1.7 cars do not have so many.

    The reason Jetronic cars had so many, is because it had an analog ECU, with very very simple control. It wasn't possible to include the cold start idle routine in the ECU. The ECU is a fixed function circuit, that takes X input from the AFM, and outputs Y to the injectors. The cold start is an independent system, with its own temperature switches, which need to trigger at different temperatures.

    Welcome to the world of state of the art 1970s era electronics!

    - - - Updated - - -

    Quote Originally Posted by superj View Post
    Uh oh, nla means eta powered cars, 3 and 5 series are going to be dropping off the road soon
    Quote Originally Posted by 1SGDHORN View Post
    What do I do when one of the sensors in no longer available? And the top is loose/fell off. I epoxied it back on, but would like to find a new one. Anyone know where these can be purchased?

    Convert to motronic.
    Last edited by earthwormjim; 04-10-2018 at 12:32 PM.

  18. #18
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    No e30s, again :(
    I just thought about taking the cold start out instead of converting.

    I actually would covert but since there are no local 325i for parts, I would have to bid against everyone and their mom and ebay to get parts and then it would cost a bunch
    No e30s again.

  19. #19
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    Quote Originally Posted by superj View Post
    I just thought about taking the cold start out instead of converting.

    I actually would covert but since there are no local 325i for parts, I would have to bid against everyone and their mom and ebay to get parts and then it would cost a bunch
    Might leave you stranded doing that. "Cold" is relative, it doesn't mean for freezing temperatures, it means when the block is not at 100 degrees Celsius.

    I guess you could crank open the throttle body a little so you always idle a little higher.

  20. #20
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    No e30s, again :(
    I thought about that, also, the temp at which is actually helps starting. and down here, on the days I would be driving to work, its at a temp where I would need the cold start because its to cold for me to bike into work
    No e30s again.

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