Sticking Revs/high idle

Discussion in '16-valve' started by Cipher, Apr 15, 2012.

  1. Cipher Forum Member

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    I've just got a new Mk2 Golf. 16v KR 1989. When I start it, it revs up to 2000rpm and then very slowly goes down to 1000rpm. When I then rev it, it will stick at that rpm and then if i rev it again it will stay at that rpm. I.e if i rev it to 2000rpm the revs don't drop, then if I were to rev it to 3000rpm it won't drop. The only way to get it to drop back down is to drive off. Also in-between gear changes the revs go up to 3000rpm and stay there.

    I can see that the cable isn't sticking when looking in the engine bay. I've checked for air leaks as well. I've also disconnected the ISV and the revs don't drop on idle.

    Anybody got any ideas?
     
  2. Cipher Forum Member

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    Just took off the intake boot before the throttle body and checked that both butterfly valves were closed, and then started it and the revs still went up higher than normal... I then disconnected the ISV wiring and the TB wiring and the revs dropped a little bit. I have also tried a working ISV off another Golf I have and no change. Would the fact that the crankcase breather is disconnected and where the breather attaches to the air box is blanked off have anything to do with it?
     
    Last edited: Apr 15, 2012
  3. Cipher Forum Member

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    Any ideas?
     
  4. bazmcc Forum Member

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    I assume the throttle cable is moving freely and the cable and pedal returns straight away to the normal position?

    Check your vac pipes on the back of the manifold, on the throttle body and all connecting pipes.

    When it's at this high idle if you nip the isv to intake pipe do the revs drop straight away?
     
  5. Cipher Forum Member

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    Throttle cable is moving freely and pedal movement is fine. If i nip the isv pipe or disconnect it sometimes the revs drop and sometimes they don't? Also tried another isv and no cure to the problem. I will check the vacuum pipes tonight
     
  6. mk2bal Forum Member

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    What about the overrun valve? Mine was holding open and doing similar things, maybe try unplugging it for now? Also be sure throttle returns fully, and hits the isv microswitch every time.. Breather will cause you no issue as long as there's defo no air getting in through the spout on airbox, make sure its 100% leak free
     
  7. Cipher Forum Member

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    Do you mean unplug an electrical connector on it? I think I'm goin to try another throttle body to make sure the switches are functioning correctly. I shall check the crankcase breather, where it has been blocked off. Thanks for your input guys, any more ideas would be appreciated!
     
  8. Gambit

    Gambit Forum Member

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    easy way to test the throttle closed micro switch is just hold throttle open by hand around 4k and press (& hold) the micro switch with finger or flat head screwdriver. if its working it'll operate the over run valve, the rev's will then momentarily plummet before rising again. with you holding the switch it'll continue to do this
     
  9. Cipher Forum Member

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    So the revs will drop even win the butterfly valves open?
     
  10. Gambit

    Gambit Forum Member

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    yes - it opens overrun cutoff valve which causes the airbox flap to momentarily shut which in turn causes the revs to plummet
     
  11. Cipher Forum Member

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    I've just checked for vacuum leaks. Where is the hose that goes to the servo? Where do it go from the inlet manifold? Ive the crankcase breather back on the air box incase there is any leaks. Seems very slightly better. Revs are not sticking at high rpm. It has been very intermittent. A lot of people have said it could be the blue temp sender.when I press the idle switch whilst revving the car there is no change?
     
  12. Gambit

    Gambit Forum Member

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    blue temp sender - thats for an 8v

    if the rev's are not dropping when you click the switch then either the switch isnt working or the overrun aint working 100%
     
  13. danster Forum Addict

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    The servo connection is on the rear of the plenum / inlet manifold on the gearbox side. There is a short flexi pipe that connects to the hard plastic pipe. This small section can deteriorate and cause air leaks.
    Also the hard plastic line that joins to the servo can rub through against the bulkhead and cause an air leak.
     
  14. Cipher Forum Member

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    So the opposite side to the throttle body on the back is the one that goes to the servo? I'll check the state of that and follow it to the servo. I'm thinking that it is more a problem with the switches as its an intermittent fault? Is the overrun locate underneath the intake boot? Would the fact that the air box has been drilled a lot have an impact on this?
     
  15. mk2bal Forum Member

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    Air box would only be a problem if drilled in the top half, above the metering flap allowing un-metered /fuel matched air to enter. Don't think sticking revs would be a symptom of this, itd probably be harder to get to run at all I'd imagine?
     
  16. Cipher Forum Member

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    It's drilled on the bottom half. I'm thinking that it's more of an electrical fault, only because it's not there all the time. I just went out in the car and the problem wasn't there, but after a few minutes it started again. Then it didn't do it and them it started again?!
     
  17. rubjonny

    rubjonny Administrator Admin

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    look closely at the idle switch, and the small linkage part that presses it. the switcvh linkage is seperate from the main throttle linkage and has its own return spring. if this gets sticky sometimes it wont press the idle switch and result in high revs. take off the 13mm nut then the linkage, spring and 2 plastic washers come off. clean it all ip and grease, then refit. be extra careful that you dont catch the spring in the washers, that'll make it stick. it should move free once done, and always return to press the switch no matter how slight the movement on the throttle pedal
     
  18. bazmcc Forum Member

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    I know this is fairly obvious but are the earth connections on the back of the head above cylinder 4 clean and well connected. I had loads of idle and running problems and it was a bad earth connection that caused it.
     
  19. Cipher Forum Member

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    Many thanks for all your input everyone. Solved the problem, the T piece connector that goes to the brake servo, two hoses had come off and perished. Cut them down and put them back on and now the problem is solved! The revs now drop much quicker and it idles much smoother, I've now adjusted the CO and idle and it is running sweet. Thanks everyone
     

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