revs staying up on closed throttle - BMW F800 Riders Forum & Registry



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  1. #1
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    newbie here,Hi Guys, recently purchased a 2008 f 800 st with 22k on the clock. For the last five years it has had little to no use. I have had to replace fuel pump last week as the original died.
    Yesterday went out for a spin and as I closed throttle for a couple down shifts before a corner the revs didn't drop !! Got round bend ok slowed down using brakes then killed ignition and coasted to a stop. Upon restarting bike everything was as normal. The bike did this a further 3 times on the way home, when I turned the key off and on again without stopping it would solve so I suspect electronic rather than mechanical problem. Any ideas. thanks in advance

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  3. #2
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    How high were the RPMs when they got stuck? I'd suspect the idle stepper motor to be faulty. It probably gets stuck in a fully open position every now and then. You can remove it and try cleaning it.

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    Quote Originally Posted by bachu View Post
    How high were the RPMs when they got stuck? I'd suspect the idle stepper motor to be faulty. It probably gets stuck in a fully open position every now and then. You can remove it and try cleaning it.
    first time it happened was heading for the red line when I pulled the clutch next couple of time seemed a little less settled at around 4k.
    so this Idle stepper motor, would it be opening if I'm at full speed "ton plus private road" say if the o2 sensor was reporting a rich mix?? or is it only active at idle.Its just that every time it happened I was at high speed , full throttle. and after killing ignition every time it corrected it self.

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  6. #4
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    the stepper motor wouldn't hold the revs as high as 5k rpm, It only drops enough to allow an idle at 1250rpm.

    If the revs are holding it could be the throttle position sensor. If you try to rev the bike (if it does it again) see if it holds the revs at the new position, or does not read the input and maintains the current level.
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    I agree, it's not the idle motor then. I think we're missing a more thorough description here.

    You say, you pulled in the clutch. Has it stopped the engine revving? You said it was heading for redline.

    I assume in all those situations the engine did indeed increase in RPM? It wasn't just the tachometer showing higher RPM?

    What exactly happened? All the situations happened upon closing the throttle? You let go of the throttle but the RPMs stayed the same or kept on increasing? What, if anything, lowered them back down?

    If the engine actually kept on running at high RPM with closed throttle I'd take a look at the throttle cable if it's not snatching on anything. It's kinda impossible for the engine to run at 4k+ RPM with minimal to no air going in.

  8. #6
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    Quote Originally Posted by bachu View Post
    I agree, it's not the idle motor then. I think we're missing a more thorough description here.

    You say, you pulled in the clutch. Has it stopped the engine revving? You said it was heading for redline.

    I assume in all those situations the engine did indeed increase in RPM? It wasn't just the tachometer showing higher RPM?

    What exactly happened? All the situations happened upon closing the throttle? You let go of the throttle but the RPMs stayed the same or kept on increasing? What, if anything, lowered them back down?

    If the engine actually kept on running at high RPM with closed throttle I'd take a look at the throttle cable if it's not snatching on anything. It's kinda impossible for the engine to run at 4k+ RPM with minimal to no air going in.
    Thanks for the help guys...when the clutch was pulled in releasing load the revs increased as if throttle was held on. after the first time, I turned off ignition while bike was still moving turned back on , restarted and revs where as normal after moving restart.

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    Throttle position sensor? That could trick it into thinking you hadn't closed the throttle. It will often reset with the computer when you turn it off/on. You can also do the key on (don't start), throttle open for 3 seconds, closed for 3 seconds, repeat 5 times, key off, then key on to start it.

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  10. #8
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    If it was the TPS but he closed the throttle then the engine would sputter and die when it tried to rev higher. With closed throttle bodies there wouldn't be enough air.

    For now I'd pull the airbox and check for any snatching (including at various handlebar positions). Heck, even the air tubes between the idle stepper motor and the throttle bodies can press on the linkage between the throttle plates and keep them open a little. I'd take extra care when putting it all back together so that the air hoses aren't interfering with anything.

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    STloon i'm having the same issue, did you solve it?

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    Quote Originally Posted by Smuzzle View Post
    STloon i'm having the same issue, did you solve it?
    Have you checked the throttle cable is operating the throttle bodies correctly? EG there is no snag in the line not causing them to react to the closure of the throttle.
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  13. #11
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    Mine problem is similar...
    when i hold the clutch lever and zeroing the throttle the rpm stays at 4K. if i rev a bit the rpm goes to normal and as soon i release the clucth goes back to 4k

  14. #12
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    sounds like an issue with either the idle control valve or the vacuum pipes.
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    Quote Originally Posted by DJ123 View Post
    sounds like an issue with either the idle control valve or the vacuum pipes.
    the previous owner did take out the 25kw kit by himself. does the ECU need to be reprogrammed after? could be that the problem?

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    Possibly - was that the one with the throttle restrictor?

    Check the throttle cables & how much they open/close.

    On closed throttle the valve should be fully closed and flat, at 100% they should be wide open at 90 degree angle from the pivot point. (hopefully that makes sense)
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  17. #15
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    Sorry for not responding sooner, Forgot my login.
    Anyway...For me it turned out to be a small rubber grommet on the cable fouling where the cable meets the carb.

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  19. #16
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    Thanks all, i did bring the bike to BMW to see what's going on....ill keep you update as soon as they call me to pick it up.

  20. #17
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    A hanging idle is the classic symptom of an air leak. Usually a crack in the rubber vibration isolator intake manifold.
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