No announcement yet.

Bosch 3 wire question - low idle on e30

  • Filter
  • Time
  • Show
Clear All
new posts

    Bosch 3 wire question - low idle on e30

    Hi everyone,

    I’m struggling with a low idle on an E30 with an m20. Smoke test done, no leaks, blue temp sensor and all other electronics tested. Tested ICV per the Bentley manual and the the center pin of the connector (pin 2) was 12 volts as it should be but when I measured the outside pins, pin one measured 9.62 volts, and 10 is the acceptable value; however, pin 3 measured 4 volts instead of 10 volts. I’m trying to figure out what pin 3 controls of the icv. When the icv is disconnected with the engine running there is no change in rpm and it appears there should be an increase in idle. Where do I go with this and what is pin 3? I’ve uploaded the Bentley manual instructions and a diagram of my results. I emailed Bosch tech support as well. I’m thankful for any help. - Tom
    Last edited by donahue1980; 02-03-2020, 08:31 AM.

    The ICV has two sets of windings that are controlled by a PWM signal from the DME on pin 1&3, if one side is 25% the other will be 75% and why the voltage shows different on those two pins. The valve is not spring loaded so unplugging it will leave the valve in the same position.

    I would check the valve is freely moving, with the valve off if you rotate it back and forth quickly you should hear/feel it hitting fully open and closed, try cleaning it if not.

    I would also check the TPS, make sure you hear a click when just coming off the throttle stop, adjust the TPS if needed (don't use the throttle stop to adjust this or the idle unless you already have).

    They also get oil build up inside and may not be making the best connection, I drill a small hole on the bottom and let it drain and spray some WD40 or equivalent. There are two switches, one for idle with a micro switch that will click and one for WOT that wont, you can check them both with a DMM.
    My M20 Frankenbuild(s)
    4 Sale - Fully Built TurnKey Megasquirt Plug and Play EMS


      Its very rare to not have any vacuum leaks on these motors unless your motor has been recently rebuilt or you proactively replaced all gaskets and hoses with brand new. If you did not have your engine rebuilt or you still have old hoses, gaskets, then I would assume the shop that did your smoke test did not do it properly. Whodwho provided some great advice so I would check his suggestions first.
      Owner - Bavarian Restoration
      BMW and European Electronics Repair and Restoration
      My Feedback Thread
      Our Facebook!
      Follow our Instagram!


        Hey OP,
        It sounds like we are chasing a similar problem. I'm troubleshooting surging idle and wants to die when engine cold, and I noticed two strange things about my ICV/ICV circuit:
        1) I also noticed the seemingly strange voltage readings you got on the ICV wire harness connector.
        voltage at the icv valve harness connector between center terminal and each outer terminals: red/wht&wht/grn-> 8.93 V, red/wht&wht/yel-> 3.77 volts-- STRANGE! should both have 10volts between each? these readings were checked on a cold engine-
        a) checked resistance for Wht/yel and wht/grn wires on ICV circuit from ECU. they both had a low reisistance of 1.5-1.8 ohms. hmmmmmmmmmmmmm - wires appear to be good.
        b) voltage at the icv valve harness connector between center termiinal and each outer terminals did not change when the engine was warm. 9.1 and 3.8 respective.
        2) I also noticed this was strange about the ICV on my car-> I warmed the engine, made sure the ICV valve was completely open and plugged in the icv valve. it completely closed shut when plugged in to the harness, when the Bently clearly says the ICV valve is supposed to only be half way closed when doing this test. - see picture

        Here is what else I troubleshooted so far.
        Smoke test (using a home made machine using mineral spirits as the oil for smoke and tested the system at around 8 psi for 20 minutes
        here is how to make a smoke machine yourself: ( and
        Smoke test results-
        (Leak 1) In the carbon can breather valve located near the C191 connector- replaced valve
        (Leak 2) Both ends of the rubber tube that holds on the ICV valve to the throttle body- replaced tube

        Pictures of my smoke machine:

        iCV valve testing:
        1) resistance across outer terminals: 44.4 Ohms
        2) resistance accross innter and outer terminals: 23.9 and 21.4 ohms
        3) voltage at the icv valve harness connector between ground and center terminal: 11.98 volts
        4) unplugged ICV valve after engine was warm and it seemed to run better. WEIRD?
        5) valve was clean, and cleaned it again, valve opens freely

        Blue Temperature sensor:
        1) tested blue temperature guage/swtich sensor-
        blue temp sensor check @ ecu loom connector cold: 1.92 x 2k on ohm meter for pins 24 and 45
        blue temp sensor check @ ecu loom connector hot: 0.266 x 2k on ohm meter for pins 24 and 45
        blue temp sensor check @ sensor pins cold: 1.92 x 2k on ohm meter
        blue temp sensor check @ sensor pins hot: 0.266 ohms x 2k setting on ohm meter

        throttle Position sensor/switch testing:
        1) 10.6 volts accross the center brn to the outside brn/blk but no voltage from brn to brn/blu
        2) reistance accross 2 and 18 when throttle turned but not 3 and 18 at Wide open throttle (WOT)
        3) Will replace TPS when I recieve a new one this week and report back my findings.

        Distributor cap testing:
        position 1, continuity pass and .08 ohms x 200 on ohm meter
        position 2, continuity pass and .08 ohms x 200 on ohm meter
        position 3, continuity pass and .06 ohms x 200 on ohm meter
        position 4, continuity pass and .08 ohms x 200 on ohm meter
        position 5, continuity pass and .08 ohms x 200 on ohm meter
        position 6, continuity pass and .08 ohms x 200 on ohm meter
        position z (coil?) , continuity pass and 15 ohms x 200 on ohm meter (normal?)

        ignition rotor: 1.16 ohms x 2k on ohm meter

        spark plugs testing and inspection:
        plug 1 (front of motor): still sparks (spark is either white or gold, see picture) and fouled and rod that meets the little finger at the top appears to be split at base (see pictures)
        plug 2: it appears that sparks and the half of the spark plug that sticks out of the engine was covered in oil when I took it out. what would cause this? oil down in spark plug socket too. could this be a vaccum leak?
        plug 3: sparks and fouled
        plug 4: sparks and paritally fouled
        plug 5: sparks and partially fouled
        plug 6 (rear of motor): sparks and minor fouling- see pic
        conclusion of spark plug check: this m20 running richy rich.

        My car: 1990 325i Alpine White 2 door manual

        Lieben Sie Schlangen ?


          Wow! I’m going to look this over and report back my findings.


            any updates?
            Lieben Sie Schlangen ?


              I've been chasing a cold idle problem for the last few weeks and I think we're probably experiencing the same thing here. My ICV is behaving the same way:

              ICV fully closed with car warm and ignition on
              ~4V middle to one side, ~10V middle to other side, ~12V middle to ground

              Things I've checked/done:
              Checked coolant temperature sensor (blue) resistance both at sensor and at ECU plug
              Checked fuel pressure regulator as outlined in Bentley
              Checked throttle position sensor continuity at sensor and ECU plug
              Smoke tested for vacuum leaks
              Adjusted throttle stop screw as outlined in Bentley (was already messed-with)
              Replaced injectors
              Replaced brake booster and master cylinder, including vacuum grommet
              Replaced intake manifold gaskets
              Replaced throttle body gasket
              Replaced bitch tube O-rings
              Replaced O2 sensor
              Tried different (Walbro) fuel pump
              Tried different ECU (526 is original, tested a 525)
              Tried different AFM
              Tried different ICV

              Both ICVs behave the same way with both ECUs.

              It sure seems to me like the ICV isn't getting the right signal from the ECU, but I don't know where to go from here.