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Stelvio idling issues

Discussion in 'Stelvio Chat & Tech' started by MotoZA, Sep 9, 2019.

  1. MotoZA

    MotoZA Just got it firing!

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    Hi all,

    Time for remote diagnostics/ideas/hints again, please...

    My Stelvio NTX (MY2012) runs like a champ as soon as it's on the move, the engine runs smoothly, no surging, dropping, nothing like that. Basically, the bike pulls like train once on the go. BUT, as soon as the rev's drop to below about 2000 rpm (for example when stopping or at parking lot speeds), she will sometimes stall, or idle very rough, other times she'll idle fine. Very intermittent behaviour.

    Mostly, the problem is that the bike won't idle constantly (cold or hot), the engine rev's surges up and down (between 1200 and 1600 rpm), sometimes it drops (misfires), I can both hear and feel this. I can see the stepper motor trying its best to get a constant idle (if I watch the throttle body tie-rod).

    My throttle bodies are synced perfectly (to within 0.5 cm Hg with my CarbMate at 3500 rpm). TPS is 4.8 deg. I also know it cannot be unbalanced throttle bodies or incorrect TPS, since the bike runs so well once on the move. Throttle bodies are clean on the inside. The bike starts very easily. Spark plug wires/cords are fastened, I have the NGK plug caps installed. No ECU or Dashboard errors. I've never touched the sacred screw or tie-rod, and they've never been touched (the sacred screw has a small tack weld that is still intact; I assume this is done at the factory).

    I've run different fuel maps (for other reasons, not sort out to idling), it makes no difference (I don't expect that it should), but even with the stock map and everything back to stock, I have the same idling issues.

    Here is a confession of sorts that may point to my problem, both my air bleeds screws are closed. Why? Since the bike struggles to idle, the vacuum changes form left to right, so I have no idea which air bleed to adjust. I remember long ago when I first synced the throttle bodies, that the one air bleed was turned out quite a bit (the right hand throttle body), but at that stage I turned it in to get balance at idle. I also used to idle quite high (at about 1600 rpm). At the time I wanted to get things "as they should be".

    In the past the bike used to idle OK (although high), but then it used to surge whilst on the go. I have the surging sorted now, but not the idling.

    Any advice or ideas on what I should try next? Could it in fact be coil or spark plug (and caps or wires) related, or perhaps the stepper motor? I think it is the air bleed screw(s), but I'm not a trained mechanic and don't have much experience, so cannot say for sure. Also, I live a 1000 miles (literally) from the nearest Guzzi dealer, so that's not an option...

    Thanks,
    William
     
  2. V700Steve

    V700Steve High Miler GT Contributor

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    It could be just dirty throttle bodies. Air bleed holes get cleaned too. Run fuel cleaner or use detergent fuel.
    Both bleed screw can end up being closed depending on the balance.
    If it's a 12'model it may have flat tappets, there is an issue also.
     
  3. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    Also clean up the stepper motor system. There is a supply line from the airbox and a good dose of carb cleaner may solve your problem.
     
  4. MotoZA

    MotoZA Just got it firing!

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    Thanks Steve/John

    To clean the throttle bodies and the stepper using carb cleaner, I have to remove the airbox, right?

    How does one clean the air bleeds without removing the throttle bodies, or do they get cleaned automatically when spraying carb cleaner into the bodies?

    All of this is done with the motor running, I presume?

    I had a look at those throttle bodies, looks like a nightmare to remove them? Don't feel like doing that if it's not required.

    Regards
     
  5. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    For the stepper, just remove the lid. There is a passage to the air supply line for the stepper. I haven't come across throttle bodies that were gummed up so I can't help you there. Spray some cleaner in and wait a minute or two. Then start the engine and spray more. It should free up the stepper to operate correctly. I've done this to several machines to cure the stalling issue they were having.
     
  6. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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    Once you have done all the above re-balance again at tick-over and you may find the air bleeds will needs adjusting, from memory you leave the RH one closed and balance using the LH. There was a Technical Bulletin a while ago about cleaning the throttle bodies. I have a valve on the stepper motor on my Breva and operate it when the engine is warm and I find the revs drops about 150rpm. The clutch switch on my bike when operated raises the rpm about 150 , i believe it acts on the stepper motor. I don't notice it with the valve operated of course.
     
    Marco Sniekers likes this.
  7. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    Actually, you balance with both air bypass screws closed. To balance idle, open the screw on the side with the greatest vacuum. Idle balance doesn't need to be perfect, just close. What really matters is the high RPM balance where you ride.
     
  8. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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    Point taken , cheers.
     
  9. canuck1969

    canuck1969 GT Reference GT Contributor

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