high idle when warm 8v gti

Discussion in '8-valve' started by eddiedebo, Feb 13, 2021.

  1. eddiedebo Forum Member

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    Hi All

    I've replaced the engine in my 89 8v and since then it's had a high idle when warm.

    I've set all the timing/idle following rubjohnnys guide and initially it runs perfect. After around 5mins the idle starts to slowly climb up. After around 10mins the idle will be around 1300rpm and it never goes down from there. If I adjust the idle screw the idle will decrease but once the car is left to cool down and started again, the idle will be too low and the car wont start or idle without throttle.

    The high idle happens without using the throttle at all, you can just start the car and leave it running for this to happen. So I don't think it's anything to do with the throttle cable.

    The ISV appears to be working as when you pinch the rubber hose to it, the idle drops. I don't know if this is a fair test of the isv functioning?

    The idle switch is clicking on closed throttle and wires look intact.

    I've changed all hoses and connectors to and from the isv.

    I've also changed the blue temp sensor and if I unplug the blue temp sensor the idle drops to where it should be.

    Has anyone seen this before and knows what is causing it? or has an idea of something I've missed?

    Any help would be much appreciated it's getting very frustrating.

    Thanks

    Andy
     
  2. Tristan Forum Junkie

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    Was your blue sensor a genuine one?
    Is the isv buzzing?
     
  3. eddiedebo Forum Member

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    Hi Tristan

    Blue temp sensor was a hella is that a genuine one?

    How obvious is the isv buzz? I've got 2 that I've tried and I wouldn't say either obviously buzz. Would it buzz with just with ignition on and I should be able to clearly hear it?
     
  4. rubjonny

    rubjonny Administrator Staff Member Admin

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    replace the oring on the idle screw if not already done, also have you performed the throttle switch checks as per my guide, hold throttle lightly open and press the WOT switch see if revs come done. should also do this on the idle switch, but WOT switch test tells you wiring back to ecu is ok at least
     
  5. eddiedebo Forum Member

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    Hi sorry for the slow reply I had some time to take a look at this today.

    I have a spare engine so I took the idle screw and o'ring off that and gave it a try. No difference.

    At the same time I also tried screwing the idle right in and adjusting the throttle position so it idles nice and the idle switch makes contact. But it made no difference the idle rose to its normal 1300rpm after a few minutes.

    I did the WOT switch test and the revs did not change...I guess this is looking like the possible culprit? I have a throttle body with switches on the spare engine. I'm tempted to switch that over and see if it makes any difference.

    I also have a spare ISV so I might chuck that on now just to see if it makes any difference.
     
  6. costel1969

    costel1969 Paid Member Paid Member

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    Chance the ISV for pig iron but I suspect it's not the culprit but it's a quick change just to eliminate it after that it's the WOT swop out.
     
  7. rubjonny

    rubjonny Administrator Staff Member Admin

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    yeah sounds like wiring from throttle switch to ecu is bad somewhere. often splits behind the inlet, when it really wants to mess with you the wires break under the wire seals in the plug so all looks fine when inspected but no contact
     
  8. eddiedebo Forum Member

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    Tried the isv. It's definitely not that as the spare one us definitely knackered engine won't idle at all just cuts out.

    I've taken the switches off the spare throttle body and I'll try those. But it looks a bit fiddly! It was hard enough to get them off the spare engine.
     
    Last edited: Feb 26, 2021
  9. eddiedebo Forum Member

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    Was too fiddly to change the switches in place. So took the throttle body off.

    First thing I spotted was a blanked off hose on the front of the throttle body was split. Cut it just past the split and pushed it back on.

    Second thing with the throttle body off it was clear there had been an impact on the bracket which holds idle/wot switch connector. It has squashed down on the connector and it was impossible to remove it. So I took the bracket off and the idle/wot switches and replaced with spares.

    Following all of this the car still idled high and was lazy going back to idle after revving. So slackened off the idle switch and adjusted the throttle position until the idle was good and making contact with the idle switch.

    It took a bit of fine adjustment but it now seems to be sorted. I've not been able to make it idle high. I've left it for today and will start it up again tomorrow to make sure. I think I'm almost in disbelief that it might finally be sorted.
     
    davkav likes this.
  10. costel1969

    costel1969 Paid Member Paid Member

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    Good stuff - fingers crossed you found the culprit.
     
  11. eddiedebo Forum Member

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    Now it's cooled down I tried it today and it's now idling low. To the point where if I turn the lights on its about the stall.

    Should I adjust it up with throttle position or idle screw?

    At least the original issue of the idle rising after 5mins is no longer happening so I'm happy about that.
     
  12. rubjonny

    rubjonny Administrator Staff Member Admin

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    now you've got idle switch working you need to put it back into setup mode and re-adjust base idle and co, then see how you go with it
     
  13. eddiedebo Forum Member

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    Reoving the blue temp sender retards the timing and it stalls.

    Do you have a recommendation of the best way to go about it in this situation?
     
    Last edited: Feb 28, 2021
  14. Tristan Forum Junkie

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    RubJonny wrote a very detailed guide for this, literally step by step, for which he doesn't get half enough credit.

    Did you follow that?
     
  15. Tristan Forum Junkie

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  16. eddiedebo Forum Member

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    I have read his guide but that isn't really the question. I had a specific issue which is partially resolved but has ended up with my idle being very low. I'm not asking how to set the idle.

    I'm asking as my idle is low removing the blue temp sensor retards the timing and stalls the engine.

    What would be the best way to get to the point where I can set the idle from this situation?
     
    Last edited: Mar 22, 2021
  17. eddiedebo Forum Member

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    I did a bit more tweaking the throttle position so it would idle when the blue sensor is removed. Then reset the base idle. I think it's there now. But it's difficult to know for sure as it idles much better hot that it does cold. Inevitably it gets hot whilst tweaking it.

    I'll let it cool down and test it later.
     
  18. Tristan Forum Junkie

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    Iirc it usually ticks over faster with the blue sensor disconnected?
    I wonder have you an ecu issue?
    They're prone to corrosion on the ecu plug and pins, could be worth having a look, they're easy to open both the case of the ecu and the plug.
     
  19. rubjonny

    rubjonny Administrator Staff Member Admin

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    make sure the ignition timing is correct first, unplug sensor hold revs and set to 6-8degrees. if the car wont idle once blue sender is off and revved 3 times then your base idle is too low, so you hold the throttle open and adjust idle and co till it'll idle nicely

    if the ignition timing is way off the revs will run away from you as you get it closer to correct so be prepared to pull out authing you wedged in the stop to hold the revs ;)
     
  20. eddiedebo Forum Member

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    I have messed with the timing slightly when I was running out of ideas. I only moved the dizzy slightly. I will get the timing light out again and reset the timing properly.

    In terms of the throttle position. As long as the idle switch it clicking should it be left alone? or is there an optimum position it should be in? As there is a fair amount of adjustment there and I'm not clear where it should sit before I set about redoing the base idle.
     

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