Mk1 ABF now starts, but idle is 'hunting' after a minute or so

Discussion in 'Engines' started by SwervinMervin, Apr 3, 2022.

  1. SwervinMervin Forum Member

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    So, the cable to the injectors allowed the car to fire up, and following a change of fuel pump relay it continued running instead of just dying a second or so later (as if it had an immobilser on it, when it does not).
    I recorded a video showing the car starting and then the revs gradually increasing from 1000 to about 1400 or so while it warmed up and then 15 secs from the end and after a blip on the throttle, it starts 'hunting'.
    My first thoughts are idle stabilisation valve or air leak more generally, but it has been a while since I touched a car. Any thoughts ?
     
  2. Tristan

    Tristan Paid Member Paid Member

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    Sounds like ISV or an air leak alright.
     
  3. rubjonny

    rubjonny Administrator Staff Member Admin

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    check idle switch and wiring round the back of the inlet for damage while there. the isv should buzz ignition on, if not check the fuse you fewd it from. wiring for the breather heater runs round the back of inlet and if allowed to short due to crisped up burnt wires back there it pops isv fuse. when you're repairing the throttle wiring the heater wires can be snipped out as unused in our market
     
  4. SwervinMervin Forum Member

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    Thanks for the replies, the ISV is buzzing and seems to be working, and the other sensors seem okay, but will check the fault memory again and watch the temps climb and make notes. The hunting is so annoying that I haven't let it heat up properly yet so am wondering if the ECU is running on previous settings / fuel trims after reading the abfbasicsettings.pdf.
    I've tried cleaning the ISV a little but have dug out the two other ISV's from previous VW's to try them if the cleaning doesn't help. Since the idle doesn't seem to be adjustable on the ABF I'm thinking ISV, air leaks, and following a read on the forum, the lambda sensor, as possible culprits (in order of likelihood).
    Does anyone have experience with a failing / failed lambda sensor and how it affects running please ? Would it show up on VAGCOM (lite) or rather where would it show up as I'm not completely sure of the 'groups' even with the label files in place (I'll upload a printscreen to show what I mean) please ?
     
    Last edited: Apr 4, 2022
  5. rubjonny

    rubjonny Administrator Staff Member Admin

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    make sure you check idle switch, they can go faulty. mine went bad intermittently and would try and pull the idle back even with throttle open which made for an interesting drive experience :lol:
     
  6. SwervinMervin Forum Member

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    Thanks again RJ, my (fabbed replacement) idle switch gives me all the right readings on a multimeter.

    Update, following a liberal spraying of WD40 and a change of the ECU to throttle body 3mm air pipe it seems to have calmed the hunting down a lot !
    Still need to run thru the basic settings when warm and read the fault codes but starting to feel as if progress is being made and was able to drive it (on private land of course :) albeit with a squealing (hopefully fan) belt.
     

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