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Thread: Idle AFM unstable

  1. #1
    Guest milsom93's Avatar
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    Idle AFM unstable

    Looking for some help chaps and chapesses,

    Iíll use todayís figures as an example but this has been happening since Rockingham last month.

    So when I start the car cold it runs at 11-12 then when it warms up to the point it the thermostat opens it will vary massively from 13-16. It doesnít jump fast, it normally transitions from around 30 seconds and I have noticed it happens a lot more when the electric cooling fan has come on (but not always) and dragging some current. When it does it, the car seems to idle rough also.

    I have tried un plugging sensors when the idle is somewhat normal to see what makes it change but nothing has. The only thing I can think of is the lambada is going whappy. I am just wondering what you guys would do next?

    Thanks in advance


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    Bad battery ground ?

    Have you unplugged the lambda sensor ?

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    Dorset & Hants Rep pointz's Avatar
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    When you start it from cold it will be in fast idle (12-1500rpm)
    When warm 850rpm so afr's will be different but possibly not that much.
    Mine used to hover around 15-16 on idle when warm.

    Have you calibrated the sensor?

    As auto says or even a bad battery.
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    Guest milsom93's Avatar
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    Quote Originally Posted by autosri View Post
    Bad battery ground ?

    Have you unplugged the lambda sensor ?
    Iíve just been out and unplugged it but I am unable to test it yet but I will report back.

    Good shout with the ground, Iíll check all the current grounding points.

    Quote Originally Posted by pointz View Post
    When you start it from cold it will be in fast idle (12-1500rpm)
    When warm 850rpm so afr's will be different but possibly not that much.
    Mine used to hover around 15-16 on idle when warm.

    Have you calibrated the sensor?

    As auto says or even a bad battery.
    Yeah I expect it to be rich on cold idle but I am suspicious that 16 is way lean. The sensor was brand new a month ago which it came with a calibration certificate so I assume the sensor is fine.

    Iíll see how the lambada unplugged makes a difference and check the ground. Thanks guys


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    Also check the exhaust is grounded
    Mine runs in the 11-12 area on choke and with a bad o2 sensor it was flicking between 14-15 quite slowly enough to just feel it then with a new sensor it sits at 14.4-14.7 flicking very quickly like it should

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    Guest R3K1355's Avatar
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    Quote Originally Posted by milsom93 View Post
    Yeah I expect it to be rich on cold idle but I am suspicious that 16 is way lean. The sensor was brand new a month ago which it came with a calibration certificate so I assume the sensor is fine.
    Is this a wideband sensor?

    Does the car also have a narrowband?

  7. #7
    Guest milsom93's Avatar
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    Quote Originally Posted by autosri View Post
    Also check the exhaust is grounded
    Mine runs in the 11-12 area on choke and with a bad o2 sensor it was flicking between 14-15 quite slowly enough to just feel it then with a new sensor it sits at 14.4-14.7 flicking very quickly like it should
    To my knowledge the exhaust isnít grounded, I didnít even realise it was a thing. Iíll put it in my check list, thank you

    Quote Originally Posted by R3K1355 View Post
    Is this a wideband sensor?

    Does the car also have a narrowband?
    Yeah AEM Wideband that I have installed, it still has the stock one too if that is a narrow band?


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    There was a ground strap I think from the factory but aslong as the exhsust studs arnt loose it should be fine

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    Dorset & Hants Rep pointz's Avatar
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    Even though it has a calibration cert do you not still need to calibrate it when fitting?
    I know with the innovate wideband your "meant" to calibrate every 6 months or so!

    16 on idle I can't see doing any harm! Mine has always been about 15-16 on idle
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    The AEM has a calibration resistor in it so there is no calibration needed

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    The ground strap bolts the head above the lambda and runs to a tag on the bulkhead.

    It grounds manifold though the studs and nuts.

  12. #12
    Guest milsom93's Avatar
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    Hi All,

    Just to let you know I unplugged the stock lambda and now it idles spot on all the time. Thanks all for your time and penitence. Suppose I best get one ordered

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