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Thread: 325e 45 degree coolant temp idle sensor INFO NEEDED

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    325e 45 degree coolant temp idle sensor INFO NEEDED

    Hey everyone, I am looking for some info about a particular sensor on the 325e thermostat housing. This sensor/switch is a 45 degree C (113 F) coolant temp sensor/switch and apparently plays a part in idle control on early model E30 engine management systems. This sensor was also apparently unobtainable until recently, you would have had to make your own sensor or just forget it. The questions I have are, how does this sensor play a part in idle control and what would the absence of this sensor (broken/faulty) cause your cars idle to do. What would the missing information from this sensor cause your car to do when closed at 113 degrees F?
    Screenshot_4.png

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    Here's a very good resource that I believe will answer any questions you may have with the specific functions of the coolant temp switch https://www.e30zone.net/e30wiki/inde...to%20the%20ECU.

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    Hey thanks for the reply, that is not the sensor I am referring to. Here is an image of it https://imgur.com/a/Pq3hFpv

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    The only thing I can find on that sensor is "Coolant Temperature switch Closed above 113F for idle speed control". The wiring diagrams show the sensor feeding the ECU and Idle Control Module.
    2004 525i Sport, Manual - 1985 325E Coupe Manual

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    Got it, I'll have to do some testing

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    2 pole switch with yellow insulator found on the thermostat housing. This switch provides input to the idle controller for warm engine operation. Switch is closed above 113 F (45 C). This is an input only for the idle control module (ICM) found in Motronic 1.0 systems. The ICM will raise the idle speed when it thinks the engine is cold (switch open).

    To test measure continuity across the terminals
    Engine cold (< ~113 F (45 C)) - switch open
    Engine warm (> ~113 F (45 C)) - switch closed
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    1986 Delphin 528e - Roof rack equipped lumber hauler.
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    So when I start my car, idle will rise with water temp until it temp hits 113 degrees F. At that point, the switch will close, and idle will return/stay at set speed?

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    Quote Originally Posted by cole45acp View Post
    So when I start my car, idle will rise with water temp until it temp hits 113 degrees F. At that point, the switch will close, and idle will return/stay at set speed?

    it's the opposite. idle comes down as the car warms. at 113f it takes the icm out of the loop and the car runs without. there's no such thing as a set idle speed.

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    Okay understood. Thanks for all the info guys, really appreciate it

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    Quote Originally Posted by cole45acp View Post
    Okay understood. Thanks for all the info guys, really appreciate it

    you're doing good. you'll figure it out no problem. e's get no love but they are real solid little engines.

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    Quote Originally Posted by cole45acp View Post
    So when I start my car, idle will rise with water temp until it temp hits 113 degrees F. At that point, the switch will close, and idle will return/stay at set speed?
    Also it's not a sensor. It's a switch; on or off.

    So cold (switch open) is high idle.
    Warm (switch closed) is normal idle.
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    1986 Delphin 528e - Roof rack equipped lumber hauler.
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    1998 Avus Blau 328iC - Soon to be sold.
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

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    Quote Originally Posted by richardodn View Post
    Also it's not a sensor. It's a switch; on or off.

    excellent point.

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    Yep, thanks again guys. I found a company that makes these 45 degree switches and purchased one a month or so ago. It came from Poland so it took awhile to get here. Tonight I measured the new switch for continuity across both terminals and I had no circuit. Put some hot water in a bowl then held the switch in and measured continuity again and had a circuit. I didn't have any doubts that the new sensor wouldn't work, I just wanted to do a little experiment. Also haven't been able to drive my E30 for a week or so but tomorrow I'll test my switch that's in the car before and after driving to see if that one does the same thing. Also, for anyone looking for a new 45 degree temp switch (THE ONE WITH YELLOW TOP) you can buy them from blackstarmanufacture.

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    nice.

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    Well update, the new 45 degree switch did not fix my idle issue. I tested the old switch and it was working exactly like the new one. But I threw the new one in and went for a drive anyway. 10 minutes of driving and no issues everything was working as it should, all of a sudden my idle starts to surge again when I pushed my clutch in at a stop light. Darn, really thought I was onto something there lol. Back to the penny!

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    Quote Originally Posted by cole45acp View Post
    Well update, the new 45 degree switch did not fix my idle issue. I tested the old switch and it was working exactly like the new one. But I threw the new one in and went for a drive anyway. 10 minutes of driving and no issues everything was working as it should, all of a sudden my idle starts to surge again when I pushed my clutch in at a stop light. Darn, really thought I was onto something there lol. Back to the penny!
    maybe check for vacuum leaks, and / or clean out the idle air control valve. iacv's are getting to be a problem as the cars age.

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    Surging idle is most likely a dirty/sticking idle air control valve (ICV).
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Soon to be sold.
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  18. #18
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    Yeah thanks guys but unfortunately Ive already been down the idle control rabbit hole several times over. I suspect a broken/faulty idle control valve too but dont have the means to finding a good known working one at the moment. Until then Ill continue to use the penny lol

  19. #19
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    The other suspect part on the early models (Motronic 1.0) is the idle control module (ICM). Motronic 1.0 had idle and engine control as separate modules and the idle module is known to have internal solder issues. Easiest thing is to swap it with a known good and see what happens. A faulty one can be repaired by reflowing the solder on the main connector.
    "Howdy, Folks!"

    1986 Delphin 528e - Roof rack equipped lumber hauler.
    1989 Zinnoberrot 325iX Sedan - I miss this car. (Deceased)
    1998 Avus Blau 328iC - Soon to be sold.
    2008 Platinum-Beige X3 3.0si - Current project
    2012 Alpine White X3 xDrive35i - My new snowmobile.
    2020 Estoril Blue 440i xDrive cabrio - This car is a blast to drive.

  20. #20
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    I have replaced mine with a rebuilt one from ProgRama in Boca Raton, FL. You definitely can't go wrong with the guys over there. I honestly just think my ICV is broken/faulty man, I'll tell you the story. My idle was a little unstable one day, looked it up and everyone said just to clean it with some carb cleaner. I sprayed it out and plugged it back in and boom idle started to surge like hell. I'm talking 700-1500 up and down. Maybe I damaged it while cleaning it? I'm not sure, I don't have the means to find a known good working one to try at the moment. I've purchased 2 "working" ones from eBay and ended up returning them because neither of them worked. The weird thing about the whole deal though is, when I cold start the car, I can drive it for about 5-10 minutes until it starts to surge. If I start the car and let it sit and idle, it will start at 700-800 and then over the course of those 5-10 minutes the idle will continue to rise and rise until it hits about 1500. Upon hitting 1500 it will then start to surge up and down infinitely.

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