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  1. #1
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    STX-15F Dies At Idle/When Throttle Lets Off

    Hi guys, hoping anyone would be willing to help me on this!

    I have a 2011 STX-15F. Recently I noticed it was pulsing a bit at idle on the hose. Thinking it might be bad plugs, I did an oil/filter change and swapped the plugs. Took it out, and it ran fine at first. A few times when I would ride at -full throttle and let off the throttle quickly, it would occasionally shut off, but not always. It would re-start no problem, but after about 20-30 more mins of riding between ⅔ and full throttle I noticed that it wouldn't even stay running at idle unless I gave it a little bit of throttle. Brought it back to the ramp, and when I went to start it after getting my trailer and dropping it in, it was fine idling back to the trailer (it was able to sit and cool off for a few mins). It was also fine running on the hose to flush it back at home. I did also notice that there was a bit of light smoke in the engine compartment when I got back to the ramp. I had recently coated the entire interior with a light spray of Seafoam Deep Creep, so I thought this might be from the spray burning off the hot motor, but I'm not sure if it could potentially be a small exhaust leak. The machine does have a smooth acceleration with no hesitation all the way up to full throttle, and it still rips pretty good for a 10 year old ski!

    So far my research is pointing me towards the ISC stepper motor, possibly a valve adjustment (it's at 225ish hours), or even a small exhaust leak. I've looked over the exhaust and didn't see anything obvious, and there's no water in the hull, but again, not totally sure. Do you guys think I'm on the right track? Any particular thing I could zone in on first?

    THANKS GUYS!


  2. #2

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    100% that damned ISC solenoid, not so much a stepper motor.. Sometimes you can clean it out and get the plunger to move freely, however most I've seen the windings in the electro magnet side get moisture in them and the tunnel swells up making it useless. Easy fix though, albeit not the cheapest.

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  4. #3
    RIWaveRunner's Avatar
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    Quote Originally Posted by Rescue1 View Post
    100% that damned ISC solenoid, not so much a stepper motor.. Sometimes you can clean it out and get the plunger to move freely, however most I've seen the windings in the electro magnet side get moisture in them and the tunnel swells up making it useless. Easy fix though, albeit not the cheapest.
    Thank you so much for the reply! Are you thinking the light smoke in the engine bay was the penetrating oil burning off or something like that? I had also recently done an oil change so could be a little bit of that burning off too from a few drips. I looked and felt around for a possible exhaust leak but really couldn't find anything, just wanted to be cautious.

    Thanks again!

  5. #4
    Could be either of those 3 things and a few more! try and determine where the smoke is coming from. if its coming from what u sprayed over the engine it should burn off quickly, as im sure you know the isc motor makes a rattling noise after you switch the machine off so if ur not hearing that you should investigate further(It can still make the noise but be gunked up inside though) also for an older stx a few years ago i replaced my isc motor with a mitsubishi part which was a direct fit at fraction of the cost

  6. #5
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    Quote Originally Posted by spikeq View Post
    Could be either of those 3 things and a few more! try and determine where the smoke is coming from. if its coming from what u sprayed over the engine it should burn off quickly, as im sure you know the isc motor makes a rattling noise after you switch the machine off so if ur not hearing that you should investigate further(It can still make the noise but be gunked up inside though) also for an older stx a few years ago i replaced my isc motor with a mitsubishi part which was a direct fit at fraction of the cost
    Thank you for the help! I actually popped the motor off today and tested the resistances as per the service manual. Most of the ones that are supposed to be "about 30 ohms" per the manual are between 30-32 (is that close enough?) and the ones that are supposed to be "about 60" are between 60-63. Forgive the ignorance, but I guess I'm a little confused as to how this thing actually works. Pic of mine is below, does the black plastic piece on the end spin or is it a plunger type motion? Right now that piece can be pushed very slightly against the spring, but it can't be spun at all by hand. Is that normal/is there a way to disassemble it further? I've combed the service manual but "replace motor" is as far as it takes me.

    Thank you guys for taking the time, truly appreciate it!

  7. #6
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  8. #7
    Plunger type movement, it controls the amount of air through the throttle body at idle to keep it steady! is it making the rattle sound after u turn the machine off? You could try plugging it in and bumping the starter without starting the motor and see what it does

  9. #8
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    OK, I'll go try that and report back. Is there a way to disassemble it further or is this as far as I'll get? I feel like when I listened last time, it still made noise, but not the long series of clicks that I was used to. More of a whirring sound, a few clicks, then a little more whirring...maybe it's stuck somewhere?

  10. #9
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    So I just tried it out. After I turn the engine over, the plunger contracts towards the body of the motor. Not all that much, about -", then it clicks a few times, then the plunger moves back to its original position (the one shown in the pic). Does that help?

  11. #10
    That sounds about right! is the channel the plunger goes into clean cause that plunger moves in there to regulate the air through the throttle body at idle! when it does idle is it the normal approx 1300 rpm? i went through all this myself! they dont seem to like a slack throttle cable either! if its idling too low there a set screw under the the throttle return spring as well that might help

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