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Thread: Bloody ICVs, easy to maintain if you do it the right way!

  1. #1
    Join Date
    Dec 2004
    Sydney, Australia

    Default Bloody ICVs, easy to maintain if you do it the right way!

    The Idle Control Valve (ICV) is a little monster that often starts working outside its design limits in aging cars.

    I've just done my 20th-odd ICV clean, so I thought I'd share what I've learned:

    In older BMWs, the ICV is often an ongoing problem. Causes strange erratic idle behaviours, poor mileage, reduced engine braking... confused ECM, all kinds of bad symptoms begin.


    The design is the same on most Motronic BMW engines; the ICV has a large, heavy electronically controlled vane that allows a limited amount of controlled airflow around the butterfly in the throttle body, via a 1" black rubber pipe connected to each side. On modern 4 and 6 cylinder engines, it is often hidden under the inlet manifold. On the V8s, it is on top and easy to get to, but under the top cover, near the throttle valve at the front of the engine.

    Controlled by a transistor in the ECM, the ICV works on a 0-5V DC voltage that **should** allow a known amount of air past the butterfly. The computer is programmed to supply a particular voltage to effect a desired RPM, within reason.

    As it works with cleaned air (after the filter), it should never get dirty or greasy. The vane inside turns slowly allowing more flow as the voltage increases, and it should operate promptly and smoothly.

    It is dead easy to test
    i. Remove, and ii. Connect Pin 1 and 3 to a variable DC supply (a small one around 200mA will do) and gradually turn the voltage from 0 to 5V. Watch the vane inside carefully as you do it. If its movement is ratcheted, or sudden, the ICV is not working to spec. Your car will be idling at erratic speeds, may be using too much fuel, not slowing down properly... etc. The thing to understand here is that the ECU makes many decisions about fuel and air ratio and it expects the ICV to be working properly. It will run the car with incorrect fuelling, and cause bad emissions and economy. Basically, your ECU will not be able to make very many correct decisions once the ICV starts misbehaving.

    Another test is to shake it in your hand whilst watching the vane through the outlet. Does it shake nimbly as a result of the motion, or is it locked up tight? If the vane does not seem light and agile in there, it is jammed and/or will need a clean.

    How to fix it:
    Everyone will tell you to clean it.
    Others will tell you to replace it, that cleaning doesn't work, or that it only works for a while
    More will tell you to clean it, it will work...

    So what do most people do?
    Clean it with WD40 and a rag.

    And what happens?
    In relatively short order, it jams up again. Arghhh!

    What do the shops do?
    Mechanics usually replace them. Well they would, wouldn't they. They're hardly paying for it, and they don't want it back again with the same problem.

    Here is how to clean it so it lasts and doesn't jam up. At least not for a very long time:

    Clean it out by flushing it briefly with petrol or kerosene:

    1. Close the outlet, fill the ICV with cleaning fluid, and close off the inlet.
    2. Hold it with the solenoid end (the electrical connector end) upmost. This will reduce the amount of fluid that might leak around the vane's shaft into the solenoid section.
    3. Shake it so the fluid inside washes the surfaces well. No need to shake violently.
    4. Drain. The internal surfaces should now be silvery clean.
    5. Do this again, but this time with a small amount of methylated spirits, or isopropyl alcohol*.

    * Skip step 5, and it will jam again at some point.

    If you now connect it to a variable DC supply, it will move freely and accurately. If it doesn't, repeat 1-5. If it doesn't move at all, check your connections, re-test or figure out if you are ready to be pronounce it dead. Maybe it will be time to throw it out and get a new one, or a junker that you can clean up ;-)

    I've never had to do this ;-)

    If you don't have a variable power supply, any battery will do, just keep the voltage below 6V. 1.5V will open it about 1/3 of the way. Or just do the above shake test again, watching the internal vane. Is it now light and flappy and moving up and down a little as you shake?

    Yes? Great. Chances are it will is ready to be put to use. Time to re-install
    No? Bah... clean again!

    Does it ever need lubrication?
    No. The vane is suspended on sintered bushes, which are self lubricating.

    What if it was oily? If someone lubed it before? Will the bushes be ok?
    Most have had this done to them.
    The oil will now be mostly gone from the surfaces, but the sintered bushes will have absorbed it and may be damaged. I've never seen this in an ICV, but it happens with all these bushes. People oil them, and they fail- at least they do when supporting a shaft that moves fast (such as in an electric motor) and probably also under heavy load. I think they overheat. Perhaps with ICVs, this just doesn't happen, or they just last a long time.

    Why do they jam up anyhow?
    They get oily from blow back (is your engine worn or running badly for other reasons?) and they also get oiled by people lubricating them. The oil catches and collects microscopic particulates from the filtered air stream, also soot from the blow back. It builds up, eventually jamming the valve.

    What about soaking it overnight?
    No need to do this, just a few flushes should bring it back to life pretty fast. If you really have to remove baked on grime, try, but make sure you use kerosene or diesel fuel and ensure the electronic/solenoid section stays clear of the fluid.

    And remember, just like your appendage, try to remember to clean it every few years to avoid stinking the place out.
    Last edited by genphreak; 03-28-2017 at 06:16 AM.

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  2. #2


    Good writeup. Thanks for sharing. My car had idle problem before, and I just cleaned the ICV valve to fix the issue.

  3. #3
    Join Date
    Oct 2014
    Oakland CA area


    Yeah, cleaning the ICV solved my idle problem, too. Unfortunately, I had just replaced the head gasket and put everything back together, only to have to remove the intake manifold to get to the ICV. Oh well, it worked out in the end. I didn't disassemble everything - just enough to move the manifold far enough to prop it on the dipstick, then I could access that very stuck ICV. I hit it with brake cleaner, then some PB Blaster, let it soak a while. Shook it and it freed up. Cleaned it some more with brake cleaner, then a bit of WD40. Works great, car runs and idles as it should. Hooray! 1995 5225i, M50TU.

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