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Thread: Rough Idle were to start

  1. #1

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    Rough Idle were to start

    So my car has been idling rough for quite some time now.

    i did a boost leak test

    found none after the turbos
    but there is a one inch hole before the front turbo and after the maf ( My guess is because the car has been fitted with a BOV one of the opening is open) ... Point A from the picture below

    Point B is were BOV is installed .. Point A and B are very close to each other .. The blue path does not exist now

    now if i plug that hole with something the idle rpm stabilize at 750 rpm this makes sense because now no extra air is begin sucked through that hole and all air comes through the maf so the fueling is correct.

    but now when i drive the car it feels weak. Like really slow . there is no acceleration at all . the car just struggles like a climber on a mountain .. almost no boost and the rpm cap at around 5-6K .. the rpms are slow to rise ..

    seems like if i plug that hole the car gets deprived of air.

    if i open that opening than the car drives fine with perfect acceleration. only the idle is bad then at around 400 rpm

    Untitled.png

    is the following link related in any way ?

    https://www.clubvr4.com/forum/showth...ere-s-the-pill

    Other info its a preface lift auto , BOV (VTA) installed .. no o2 sensor as it is a pre face lift.. i do have evoscan in case you guys need any thing from those logs

    thanks in advance
    Last edited by iftekhar.frt; 13-06-2019 at 07:47 AM.

  2. #2
    TAR's Avatar

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    Quote Originally Posted by iftekhar.frt View Post
    no o2 sensor as it is a pre face lift..
    All VR4's were fitted with an O2 sensor regardless of age.
    '97 Manual Legnum in silver with some subtle mods

    My first VR4 - '97 Legnum Dark Green & mean ...it was love at first sight - now sold

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    Nick Mann's Avatar

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    Has your car been remapped?

    The hole needs to be plugged, as you are drawing in unfiltered and unmeasured air.

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    Quote Originally Posted by Nick Mann View Post
    Has your car been remapped?

    The hole needs to be plugged, as you are drawing in unfiltered and unmeasured air.
    No its on original map .. exactly thats the right thing to do. but if i do that the car bogs down .. there is no power at all .. barely accelerates .. does not cross 60KPH

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    Quote Originally Posted by TAR View Post
    All VR4's were fitted with an O2 sensor regardless of age.
    mine does not .. the exhaust hole is blocked .. do you know the part number for it ? .. OEM will probably be expensive.. any cheap alternates ?
    Last edited by iftekhar.frt; 13-06-2019 at 07:46 AM.

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    MD189008

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    So any idea why no power when I plug the hole ?

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    What's your fuel economy like? Can't imagine the ECU's very happy to provide correct fuelling without an O2 sensor input.
    October 2023 fleet status: 100% operational


    | Legnum VR-4S | Fiat Panda 100HP !! | a blue one! | Avensis T-180 | VR-4 parts van! |

    Why not become a full member of CVR4 and enjoy the additional benefits membership brings?! Information here.

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    6 kmpl

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    Quote Originally Posted by iftekhar.frt View Post
    So any idea why no power when I plug the hole ?
    Any thoughts guys

  11. #11
    Davezj's Avatar

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    You need to put the car back to factory spec for the pipework and sensors. Then test the car.
    If it still not working correctly then it It could be a MAF issue.
    Is the MAF plugged in for starters.

    Bye for Now!

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    Yes the maf is plugged in . i have tried putting the pipework back but that makes the car worse ... can only a missing o2 sensor make that much issue . here is my car compared a friends car that car is also stock

    At this point the hole i explained is unplugged and the there is no o2 sensor

    1) https://drive.google.com/open?id=1Sa...45B4I62a2hP3w1
    2) https://drive.google.com/open?id=1on...Ix_2gFxxWzdk4Q

    some youtube video (bottom one is mine )

    3) https://drive.google.com/open?id=13T...e3nTfM_4yV-BT9
    Last edited by iftekhar.frt; 17-06-2019 at 03:31 PM.

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    Quote Originally Posted by iftekhar.frt View Post
    Any thoughts guys
    Is it possible your car is running so rich due to having no 02 it can't get out of its own way.
    Then once you unplug the hole the extra air is leaning it out giving it the extra power you feel
    possibly the clubs first manual super

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    Quote Originally Posted by lancerevo3 View Post
    Is it possible your car is running so rich due to having no 02 it can't get out of its own way.
    Then once you unplug the hole the extra air is leaning it out giving it the extra power you feel
    not that i am an expert on fuel ratio but the drastic loss of power by plugging that hole is un understandable for me. ( So i dont believe that running rich is causing this issue)

    A thoery was

    When the O2 sensor is off .. the car is already overfueling ... so the fuel gets maxed out at some maf value which is less the max value of maf .. so when that threshold crosses for the maf the car cant fuel more and it is actually running lean

    i do have a wide band in my honda .. should i try that ?
    Last edited by iftekhar.frt; 17-06-2019 at 03:35 PM.

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    is there a sure shot way of testing a maf sensor ?

    what could be the problems with a maf

    1) They Work or not work
    2) or can they partially work

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    Quote Originally Posted by iftekhar.frt View Post
    not that i am an expert on fuel ratio but the drastic loss of power by plugging that hole is un understandable for me. ( So i dont believe that running rich is causing this issue)

    A thoery was

    When the O2 sensor is off .. the car is already overfueling ... so the fuel gets maxed out at some maf value which is less the max value of maf .. so when that threshold crosses for the maf the car cant fuel more
    That's what I am saying as you have no 02 sensor the car is dumping fuel in to stay safe which in turn will cause it to lose power.
    Then when you unplug the hole you are letting in extra air which will lean out the mixture given you an increase in power.
    Running too Rich will cause a power loss ,running too lean will kill an engine

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    does any one have a rpm to maf value chart or can anyone datalog that with evo scan

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    Take a look at the Banks Power videos on youtube for a better explanation, but...

    The MAF is measuring grammes of air per second, the weight is dependant on the pressure, temperature, humidity and flow rate.
    If you can accurately measure the local air conditions at the intake then that can be combined with the displacement and the engine speed and an efficiency factor to calculate expected flow.
    The manifold vacuum / boost can be used to give a really rough guess at the efficiency.

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    i have asked this previously also does any one have a picture of the cars center tunnel from the inside or outside .. i cant seem to find the connector where the o2 sensor plugs in ... i bought a new o2 sensor but need to figure out how to connect it ..

  20. #20
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    I don't have a photo, but it is behind the panel to the right of the glovebox, by the passengers right calf. It is a four wire socket in white plastic with the pins in a single row.

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