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Thread: wierd idle revs

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    Racing Driver Scotty's Avatar
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    Mines jumps about like and jack in the box on cold and warm idle! Needle never stays still! I also get higher revs on every start up touching 1200 revs for 10-15 sec then it settles! I occasionally get higher rev just cause!!! Sits at 950-1000 constantly on tick over but it's not doing a regen!! Read my Need Advice, New Sottware threads and you'll see the hassle I'm having!! Mines started off just with a slight wobble!!

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    Street Racer DeaniFLHT's Avatar
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    KimboSig, on 12 February 2013 - 08:49 AM, said:
    Still getting this strange wobble between 850 - 900 revs on idle after startup. Anyone else had this?

    I honestly don't think I'd be worried about so small a variation on its own. I'm pretty sure Vauxhall/Opel would say it is within normal tolerances. (Not that everybody on here will trust their opinion).

    There are so many sensor inputs to the ECU that may have an impact on idle control, and it could be any combination of conditions that could cause the idle speed to vary.



    If you are also noticing any new or abnormal vibration, difficulty changing gear, and/or inconsistent clutch operation, then I might suspect that the dual-mass flywheel is showing early signs of wear.

    The engine speed sensor takes its signal from the flywheel. Excess free movement in the flywheel assembly can result in unstable idle control.
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    Street Racer DeaniFLHT's Avatar
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    I can't say what the expected service life of a DMF is.

    In the short time that I have been a forum member, the DMF has been a recurring topic. And service life seems to be pretty variable.

    There have been some failures reported within as little as 10,000 miles. Other cars have gone well in excess of 60,000 miles without a problem.



    The problem is not confined to Vauxhall diesel models. Diesel models from other manufacturers suffer the issue to some degree or other.

    It just appears from forum comments, that the Insignia may be more prone to the issue than some.



    Driving style, and the type of duty the car is put to, can have a big impact on the durability of the DMF.



    A lot of stop and go town mileage will be harder on the DMF than long distances at steady high speed on the motorway.



    Economy minded drivers will aim to operate their cars in the highest gear practical and will tend to short shift at quite low rpm, say 1400 - 1600 rpm and may be operating in 30mph town traffic in 4th or 5th gear at about 1300rpm.

    This practice is fine for fuel economy, but it means that the engine is labouring at the bottom of its effective torque range and loads the transmission quite heavily with low frequency power pulses.

    To reduce wear on the transmission and reduce vibration throughout the drive line, the DMF is designed to damp/smooth out these pulses. With the type of driving mentioned above, the DMF is having to work quite hard all the time and so will tend to fail sooner.

    The problem is possibly worse on Ecoflex models. As they are generally higher geared, they can travel at motorway speeds and still only be turning at 1500rpm or less, potentially putting more strain on the DMF.



    I have recently seen a guidance note about modifying driving habits to extend DMF service life. I can't remember if it was posted on I.E. or as a link to somewhere else.

    Briefly, it advocated the following:-In general, when at constant speeds, try to operate the car in an appropriate gear for the speed, so as to keep the engine speed at or above 1800rpm.


    Accelerate and decelerate gently to reduce "shunt" backwards and forwards through the transmission. Avoid the "traffic light grand prix"


    When accelerating, make upward gear changes at around 1900 - 2000 rpm and allow the engine revs to drop back to around 1500rpm as the clutch is gently re-engaged having selected the next higher gear.


    Conversely, when decelerating, change down to the next lower gear as the engine speed drops to 1500rpm, and "blip" the throttle to bring the engine speed back up to around 1900 rpm, before gently re-engaging the clutch.


    Don't let the engine labour unnecessarily on steep inclines. Be ready to select a lower gear, rather than simply putting the foot on the throttle to maintain speed.
    Thats enough lecturing from me! :P/>
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    Learner Driver sinless's Avatar
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    DeaniFLHT, on 14 February 2013 - 12:40 AM, said:
    I honestly don't think I'd be worried about so small a variation on its own. I'm pretty sure Vauxhall/Opel would say it is within normal tolerances. (Not that everybody on here will trust their opinion).

    There are so many sensor inputs to the ECU that may have an impact on idle control, and it could be any combination of conditions that could cause the idle speed to vary.



    If you are also noticing any new or abnormal vibration, difficulty changing gear, and/or inconsistent clutch operation, then I might suspect that the dual-mass flywheel is showing early signs of wear.

    The engine speed sensor takes its signal from the flywheel. Excess free movement in the flywheel assembly can result in unstable idle control.

    andy-g, on 14 February 2013 - 01:01 AM, said:
    ^^^ he's got a point on the flywheel ^^^

    andy-g, on 14 February 2013 - 09:06 PM, said:
    DMF's are shit mate , they'll go when they feel like it !!



    as the op said, there is humming noise coming from the engine and the rev needle moves like the humming, in the same rate. The neddle settles down when the engine is warm, but occasionally, it jumps from time to time. Mine, never stayed on 900, somewhere between 900 and 1000. The car has a slightly judder to say so, when is cold, exactly in the same rate as the needle moves. Been to the mechanic, told me it`s the DMF but it will still go for another few thousand miles....

    Additionally, you can hear a noise coming from the same area where the DMF is, hard to describe, like you rub 2 sheets of paper against each other, in the same rate as the needle goes.

    On the motorway, when you accelerate, you can feel a judder, like a wobble, but nothing else than that.

    I`ve had the car since last year, 97k on the clock, now it`s 103k??and still going. Maybe I will decide to go to change the DMF, but I feel so uncertain about it so....we will see !!!



    I might be something else, but from what i read .... that`s where I am going. I am no mechanic though ...so I cant tell you for sure !!!

 

 

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