ISV - idle high plugged in, normal unplugged

Discussion in 'K-Jetronic OEM injection' started by MJA, Oct 21, 2021.

  1. MJA

    MJA Paid Member Paid Member

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    Hi,

    I've been investigating a fault with the k-jet system following the guides and posts on here on my mk2 16v. It's an ABF block and head with the original KR inlet and fuelling.

    I've been through the wiring and vacuum system. I've sprayed carb cleaner looking for leaks on vac lines, around the injectors and manifold to no avail.

    My idle is at 1200rpm regardless of how warm or cold the engine is. The ISV buzzes normally I think on ignition. The idle screw is almost as far in as it will go to achieve the 1200rpm. If I go 1 and half turns out which i believe is a good starting point my idle is 1500rpm. I have not played with the fuel mix 3mm allen key yet and I've also bought a new idle screw (awaiting post) incase my seal is perished.

    If I disconnect the ISV when I am at 1200rpm the idle drops to a smooth enough 950rpm. If i plug it back in whilst it is running the idle remains at 950rpm. If I turn the car off and back on the idle goes back to 1200rpm.

    I'm going to down a path of thinking something is wrong with the ISV system, whether it controller related or the ISV itself. I have cleaned the ISV with carb cleaner whilst it was running on ignition.

    The timing is good on the cambelt side and I've changed the timing belt and tensioner ( and waterpump, thermostat etc) but no change on the running issue. I don't have a strobe light to set timing on the gearbox side so will eventually need to take this car to a specialist for a good tune up.

    Cheers for any insight

    Matt
     
  2. rubjonny

    rubjonny Administrator Staff Member Admin

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    check the idle switch is clicking throttle closed, and you see 12v on the black/yellow wire to the ecu and the isv control unit ignition on, throttle closed. push the throttle pedal a few times and release. make sure you always see 12v every time throttle closed no matter how gently you back off the throttle

    check the air shrouded injector system as well, if you havent refurbed all the injector seals you may have an air leak here, or you have but used non-shrouded type injectors you get a massive air leak past the tips, either way to rule that out pinch closed the small hose between the block breather and the nipple on the inlet between cylinders 1 & 2 or the 5th injector housing depending on what setup you have
     
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  3. rubjonny

    rubjonny Administrator Staff Member Admin

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    oh and get on ebay, find yourself a used inductive pickup timing light. if you shop around will be able to pick one up for peanuts
     
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  4. MJA

    MJA Paid Member Paid Member

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    I did forgot to mention - is the idle switch that little microswitch on the throttle body? I have disconnected that whilst running and no difference to idle and I've also rev'd to 2k rpm and pressed the switch by hand and no change - I will test it's power next as you say.

    If i disconnect the micro switch and the ISV it stalls straight away.

    And cheers for the tip on the timing light i will have a look had thought they were much more ££

    All my cars prior to this have been ECU controlled and never thought about this side of things before.
     
  5. rubjonny

    rubjonny Administrator Staff Member Admin

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    yep the black/yellow wire on throttle microswitch is for idle control, white wire cold throttle enrichment and the black wire should be ignition live
     
  6. BRI

    bri Forum Member

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    My kr 16v did the very same , I checked everything on the engine inside out trying to find the problom ,it turned out the isv was passing excessive air at idle .squeeze the hose closed leaving the isv and see if this reduces the idle .
    I just leave mine unplugged now .runs fine !
     

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