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    #1

    Another M20 Idle surge

    Hey guys yes I"ve been searching and can't find a definite answer. Besides the Fact I have a regular ETA e28 with a really bad idle surge. It starts up idles at 2000rpms for about 10 seconds then surges from 700 rpms to 1700 and keeps repeating. I thought it was a bad ICV but when I connect the ICV to a 12v battery it clicks on and off, so it has continuity and would cycle correctly. I then tested the TPS which I figured was not going into Idle mode both idle mode and WOT are working properly and I adjusted it and checked continuity and it is sending the Idle signal when the throttle is closed.

    I started the car up and unplugged the ICV and the car runs the exact same as when its plugged in and I'm getting a reading of 1.2V at the ICV plug. It consistently stays at 1.2V weather the throttle is closed halfway open, or wide open.

    Is this a DME/ECU problem? Also when I drive the car long periods of time the ICV will kick for a minute or two then stop working again intermittently.
    Last edited by foundation982; 01-01-2014, 11:37 AM.
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    #2
    ICV's are notoriously senile even when they have continuity, but I'm betting on an intake leak.
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      #3
      Try hitting the ICV with hammer while the car is running. See if something changes. I am pretty sure ICV is at fault. I had similar problems.

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        #4
        I still think it is the ECU, I energized the ICV directly from the 12v battery and the car immediately dies. I then Put a small tail light bulb between the positive of the battery and to the ICV, the light bulb added resistance to bring the Volts down on the ICV and the car idles perfectly at 850 rpms.

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          #5
          In e30 ETA's there is a coolant temp sensor called the idle control switch iirc. If it is bad, it will keep the idle control system from working properly. It actually screwed up other tests, and the idle control unit would switch on and off over and over causing the surging idle. I had the same issue, and after checking everything else several times, bought the sensor from the dealer, and enjoyed silky smooth idles.

          The idle control system on the ETA's are great when they work, but have no ability to compensate for bad sensors, and can act very wonky as a result.

          Everyone always says smoke test for vacuum leaks first, which is fine if you have access to a tester, but a couple hours with a cold engine, a volt meter, and the Bentley manual, and you can rule out everything else first.

          Sent from my Galaxy Nexus using Tapatalk

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            #6
            Originally posted by Andy.B View Post
            In e30 ETA's there is a coolant temp sensor called the idle control switch iirc. If it is bad, it will keep the idle control system from working properly. It actually screwed up other tests, and the idle control unit would switch on and off over and over causing the surging idle. I had the same issue, and after checking everything else several times, bought the sensor from the dealer, and enjoyed silky smooth idles.

            The idle control system on the ETA's are great when they work, but have no ability to compensate for bad sensors, and can act very wonky as a result.

            Everyone always says smoke test for vacuum leaks first, which is fine if you have access to a tester, but a couple hours with a cold engine, a volt meter, and the Bentley manual, and you can rule out everything else first.

            Sent from my Galaxy Nexus using Tapatalk
            hmm that sounds like a very plausible culprit, I'm gonna replace it because it's easy and cheap. But what exactly does the temperature switch do? Can't find much information on here about it. is there any way to test to see if it's working? It only has one tab which I assume is a ground can I check for resistance? (PS I will be ordering a Bentley with the Temperature switch)

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              #7
              Of the two sensors, the one with only one pin is a thermo time switch which controls the child start injector. The temp sensor for the idle circuit has two pins. You well have to check realoem carefully to make sure you get the right part number, as descriptions on pelican/etc online catalogs can be vague.

              Sent from my Galaxy Nexus using Tapatalk

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                #8
                Originally posted by Andy.B View Post
                Of the two sensors, the one with only one pin is a thermo time switch which controls the child start injector. The temp sensor for the idle circuit has two pins. You well have to check realoem carefully to make sure you get the right part number, as descriptions on pelican/etc online catalogs can be vague.

                Sent from my Galaxy Nexus using Tapatalk
                Okay sweet, gonna check the switch tomorrow when I get some free time. In the mean time I shoved a fuel hose with a 1/4inch center in the hose between the ICV and throttle body elbow idles perfectly at 750rpms! (yes this is only temporary as this is my DD)

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