BX 16 Valve high idle
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  1. #1
    Fellow Frogger!
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    Default BX 16 Valve high idle

    Hi All,

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    Since an oil change on the weekend that necessitated removal of the inlet manifold (due to the bloody oil filler hose tearing clean in half ), the car is idling at between 2k & 2.5k rpm. The only things I can think could be causing this is loose manifold bolts - highly unlikely - or the idle stepper motor that sits on top of the manifold. Is it common for these to fail/need maintenance? Any other potential causes? I would have thought that the only problematic air leaks would have to come after the throttle body.

  2. #2
    1000+ Posts Ken W's Avatar
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    Did you remember to reconnect the cannister purge valve onto the bottom of the manifold near the throttle body?

    Cheers,

    Ken W

  3. #3
    Fellow Frogger! ARCHRIVAL's Avatar
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    stepper squirt a bit of silicon spray on the pivot and cable .The cable location and free-ness can have a bearing I always just let it flop about ,as soon as it is secured it seems to bind
    Quote Originally Posted by LeRob View Post
    Hi All,

    Since an oil change on the weekend that necessitated removal of the inlet manifold (due to the bloody oil filler hose tearing clean in half ), the car is idling at between 2k & 2.5k rpm. The only things I can think could be causing this is loose manifold bolts - highly unlikely - or the idle stepper motor that sits on top of the manifold. Is it common for these to fail/need maintenance? Any other potential causes? I would have thought that the only problematic air leaks would have to come after the throttle body.
    BX 16v 89, I Renault Floride 62, Volvo P1800 68, Aston Martin DB6 68, Daimler 250V8 68, Jaguar XJC 76, Falcon Ute XL 62, Falcon Ute XY 4WD, Jeep Grand Larado 03, Mazda 6 Wagon 05, inter 483 tractor 86, makita cordless drill CX TURBO its dented D Special 1 62 ID192000 Xantia V6 2000 Cadillac STS stolen by the princess,KANGA 720DL LOADER

  4. #4
    Fellow Frogger!
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    Hi Ken,

    If that is the small module and hose that runs off to the driver's side and disappears into the front wing by the main wiring loom, I can confirm that it was reconnected. I'll double check the connection though.

    AR, don't know what you're referring to with cable actuation as the only thing would be the throttle body, which definitely isn't sticky and the cable has a little bit of slack at rest

    Thanks.
    Last edited by LeRob; 14th May 2013 at 05:44 PM.

  5. #5
    1000+ Posts Ken W's Avatar
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    LeRob,

    Sounds like you have that bit under control. I did have the valve stick open on the BX TZI once which was interesting.

    Have you tried unplugging and replugging the idle control motor while the engine is running? Its fun and that might tell you something.

    Another hope would be to flash out the ECU codes to see if it has stored any. Probably not tho. You can tell if there are any codes there because ECU light will stay on for a few seconds after engine has started. If no codes ECU goes out as soon as engine starts.

    Run out of suggestions for the moment.

    Cheers,

    Ken W

  6. #6
    Fellow Frogger! renault12's Avatar
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    Silly question.. But did you replace the broken oil filler hose? These are incredibly sensitive to leaks on the Motronic system with the symptoms of a leak being a high idle..

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    Check the connection on the temp sender under the t/ stat housing ,douse it appear to be running rich, ecu could be getting message that the engine is cold ,increasing idle speed .pugs, or its sucking air as mentioned

  8. #8
    1000+ Posts cav91's Avatar
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    Has it got a vacuum leak?
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  9. #9
    1000+ Posts PeterT's Avatar
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    I'd be going with either faulty connection to the ICV or the TPS switch needs resetting for idle.

    If there is no connection to the ICV it has a fail safe setting of letting some air through.

    '92 205 Mi16
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  10. #10
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    Turns out it was a pinched sensor wire on replacement of intake. Ran sweet as a nut today
    '92 BX 16Valve (Bathurst 12 Hr edition)
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  11. #11
    Fellow Frogger! frog's Avatar
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    I still have this problem with my car on and off. I've had it since before I replaced the engine.

    I had replaced the ICV, ECU, cleaned the throttle body, checked for vacuum/intake leaks, cleaned the AFM and all plugs etc all before swapping the engine and the problem persists.

    I thought putting a known good engine (with all of its sensors) may fix the problem but it hasn't.

    When the car is warm, driving for say 10 minutes the idle will sometimes slowly increase from normal up to anywhere below 3000rpm. No ECU codes to give any hints. This can either last for the rest of the drive or it can resolve it self straight away.
    Nothing seems to reliably fix it, no changes in driving style, or restarting the car etc.

    The problem is transient, occasionally it won't happen at all for a few trips and then it is back again. Maybe it happens more often in hot weather/summer, though I am not sure.

    Could this be a wiring loom problem? It's about the only thing that has not been replaced..
    Any suggestions on diagnosing the problem. Occasionally when I arrive home it will still be idling high, what can I check, disconnect etc at these times?

  12. #12
    1000+ Posts PeterT's Avatar
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    Have you set the idle position switch correctly? It may also be that the contacts in the switch are worn/broken. I can send you a document via email outlining the procedure if you like.

    '92 205 Mi16
    '90 Mi16x4

  13. #13
    Fellow Frogger! frog's Avatar
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    Ta Peter, that would be great.

  14. #14
    Fellow Frogger!
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    Quote Originally Posted by frog View Post
    I still have this problem with my car on and off. I've had it since before I replaced the engine.

    I had replaced the ICV, ECU, cleaned the throttle body, checked for vacuum/intake leaks, cleaned the AFM and all plugs etc all before swapping the engine and the problem persists.

    I thought putting a known good engine (with all of its sensors) may fix the problem but it hasn't.

    When the car is warm, driving for say 10 minutes the idle will sometimes slowly increase from normal up to anywhere below 3000rpm. No ECU codes to give any hints. This can either last for the rest of the drive or it can resolve it self straight away.
    Nothing seems to reliably fix it, no changes in driving style, or restarting the car etc.

    The problem is transient, occasionally it won't happen at all for a few trips and then it is back again. Maybe it happens more often in hot weather/summer, though I am not sure.

    Could this be a wiring loom problem? It's about the only thing that has not been replaced..
    Any suggestions on diagnosing the problem. Occasionally when I arrive home it will still be idling high, what can I check, disconnect etc at these times?
    This usually sets in during driving? I have what seems to be almost exactly the same problem, although I haven't gone to many lengths to investigate yet. Peter, if you could send me a copy of the doc also that would be great. Email addy PM'd

  15. #15
    1000+ Posts Ken W's Avatar
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    Frog and I are making some progress with the high idle issue. As well as making sure the throttle stop switch is correctly set, it is necessary to have enough slack in the accelerator cable so that the butterfly can reliably return to the closed position.

    Also, I think there can be a problem with the inadequate earthing of the ECU wiring loom on the engine that ends up lifting the 'ground' voltage from the throttle stop sensor to above the threshold that the ECU interprets as ground. I have had some success in correcting a number of ECU gremlins by adding a supplementary earth wire between the engine earthing point (on the fuel rail of a BX) and the battery negative terminal. If this doesn't solve the problem long term, I think I will have to attack the leads to the idle valve with an oscilloscope to find out what is really going on.

    This supplementary earthing technique has also seemed to help in a Xantia 2.0l 16V RFV engine with an MP5.2 ECU where the ECU loom seems to earth by itself to a point on the gearbox. I can't track where the battery earth return from engine gearbox connects as it seems to disappear into the engine fuse box.

    I would be interested in others comments.

    Cheers,

    Ken W

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