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Thread: Egine runs on when throttle closed, any thoughts?

  1. #1
    apriliaforum expert Apriliain's Avatar
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    Egine runs on when throttle closed, any thoughts?

    I replaced the throttle return cable a few weeks ago, i am not sure if this is related as i have double checked that it has enough free play, which it has.

    Symptoms are when riding i shut the throttle and the bike runs on as if the throttle is sticky, it is not, if i pull the clutch in it drops the revs quickly as it should, i rechecked the cables etc and all seems fine.

    It performs as it should apart from the engine running on when on a closed throttle, it does slow down but it takes longer than it should do.

    Any thoughts as i am off on a long trip in a couple of days.

    Cheers peeps
    I used to be indecisive......now i am not so sure

  2. #2
    apriliaforum expert meanstrk's Avatar
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    Do a throttle position sensor reset.
    Ron
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  3. #3
    apriliaforum expert Motech's Avatar
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    Quote Originally Posted by meanstrk View Post
    Do a throttle position sensor reset.
    ^ This. ^

    The TPS got slightly skewed during your repairs, tells ECU throttle is partially open when you close it.

    That, or it IS partially open from your work.
    No Matter Where You Are, There You Go!

  4. #4
    apriliaforum expert commandodave's Avatar
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    Check your vacuum lines. I had a problem last year (or the year before) where once the engine was warm, the idle stayed around 3K RPM. Put a load on the engine while at a stop, the idle would drop to 1200 RPM. Add throttle, then repeat. I tried cleaning the stepper motor, syncing, ad nauseum. Problem would go away for a day. Eventually I hit on replacing all the vacuum lines as they were 10 years old anyway. And brittle! Any time you dick with an old vacuum line you run the risk of causing a leak. The problem was also somewhat ambient temperature related. On the 65-70 deg F ride to work in the morning, all was well. On the 85-90 deg F ride home the problem would resurface.

  5. #5
    apriliaforum expert Apriliain's Avatar
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    Cheers guys, the TPS reset, i have no tune ecu cable and am a long way from an Aprilia dealer, is my option trying this full throttle, then ignition on reset i am reading about?

    Everything else about the idle etc. is fine, the bike is running good apart from the engine running on on a closed throttle.
    I used to be indecisive......now i am not so sure

  6. #6
    apriliaforum expert deefred's Avatar
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    Can you check your vacuum synch?
    If out of synch then it can be a vacuum leak.
    Try the reset procedure as it cannot harm.
    No guarantee for success however.
    2001 RST Futura in stream Silver.
    Mods: Modified Öhlins fork from mille R, EBC brake discs, HEL front brakelines, Carbon RS 250 front fender, Wiring mod for charging. Engine related:05 map, Iridium plugs, tuneboy, derestriced intake, old mille airboot, staintunes exhaust. Lambda bung hardbrazed in the "breadbox". Öhlins mille R rear shock with 110N/mm spring and the integrated hydraulic preload adjuster. LED Voltmeter installed inside the dash for monitoring charging. Duc 999 radial m/c for brake and clutch. EBC 320mm brake discs
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  7. #7
    apriliaforum expert RAS's Avatar
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    I had a similar problem last fall that took lubing both cables and the pulley/spring assembly at the front of the TB to fix.

    Wouldn't hurt to clean the inside of the TB bore if it's not been done in a while.

    It was fine before you changed the cable. I'd go back to that spot to have another look. Maybe the pull cable is hanging up. Sounds like you've given the return cable a lot of slack. Well, if there's too much slack, you won't be able to pull the throttle shut with it if the pull cable or throttle plates are hanging up.

    And while yer in there, have a look at those old hoses.

  8. #8
    Honest always, feared often Micah / AF1 Racing's Avatar
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    Check your idle air controller and lines/hoses going to it, also check seal of vacuum operated slipper clutch hose.
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  9. #9
    apriliaforum expert
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    Replaced the clear vacuum lines under the air box when I had this issue. They were as brittle as fresh potato chips!
    Bill
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    38K miles + 30K kms

  10. #10
    apriliaforum expert Apriliain's Avatar
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    Cheers guys, i am back from my trip, the bike ran faultless for 800 miles apart from the running on with a closed throttle, before i left i tried the open throttle, ignition on reset thing to no avail, worth a try for all the time it took.

    Anyway, the symptoms are still there, bike starts, idles at 1250 smoothly, no surging, in fact nothing un-towards apart from the motor running on with the throttle shut, makes the bike a bit difficult to ride plus i probably now need some new brake pads.

    I have just pulled the airbox off and inspected the clear lines, they all seem to be in good order, not brittle or any signs of cracks/splits, the slipper clutch hose that micah mentioned, is that the hose on the side of the clutch housing and where does it run to to inspect it?

    Stepper motor seems to be functioning as it should also, so any further help would be appreciated guys
    I used to be indecisive......now i am not so sure

  11. #11
    apriliaforum expert deefred's Avatar
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    How about removing the hoses from the stepper and plug them and see if you have the same problem.
    If you do then at least it is not the stepper which is causing this.
    2001 RST Futura in stream Silver.
    Mods: Modified Öhlins fork from mille R, EBC brake discs, HEL front brakelines, Carbon RS 250 front fender, Wiring mod for charging. Engine related:05 map, Iridium plugs, tuneboy, derestriced intake, old mille airboot, staintunes exhaust. Lambda bung hardbrazed in the "breadbox". Öhlins mille R rear shock with 110N/mm spring and the integrated hydraulic preload adjuster. LED Voltmeter installed inside the dash for monitoring charging. Duc 999 radial m/c for brake and clutch. EBC 320mm brake discs
    NWS hugger. Equipment: Famsa tankbag,
    CBR 600 -07 MOSFET R&R FH008EE providing stable 14.4 - 14.5 V (with my wiring mod). Daytona heated grips with mccoi pwm controller and automatic chain oiler

  12. #12
    apriliaforum expert RAS's Avatar
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    When this sort of thing happened to me last year, if I raised the RPMs just a bit - say to 2k, the idle would return. But if I opened the throttle more, it would hang up. With the lid to the airbox off, I could see the throttle plates not closing as the flow of air into the motor was holding them open if I'd opened the throttle enough. With slack in the return cable, the return spring alone is fully shutting those throttle plates- and they must be fully closed. You can slam the throttle shut at the bar but if the mechanism has too much friction, the plates will stay open - and it doesn't take much to raise the RPMs substantially.

    Using a very light spray lube (silicone + teflon) into both cables and at the pulley/spring assembly fixed it and it hasn't returned since.

    Makes for lousy shifting when the revs don't drop as timing is all messed up. Thought something was failing in the gearbox or clutch initially

  13. #13
    apriliaforum expert Motech's Avatar
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    Deefred's suggestion is a good one, blocking off stepper lines and seeing what idle does. In theory, idle should drop notably like that. If it does not, then there is probably a vacuum leak somewhere you could pinpoint with propane flow, stepper electrical plug disconnected.

    If idle does drop below 1K, it does indicate stepper the cause of high idle, but not necessarily the problem. If, for example, TPS value is showing part-throttle when closed, ECM will command stepper to hold higher RPMs. So, if you pinch off stepper hoses and RPM drops, first reboot: shut off engine and reconnect everything to normal. Then restart and manipulate throttle until you get you high, closed-throttle RPM symptom back again. With high RPMs present, rap on side of the stepper motor sharply a few times with screwdriver handle. If RPMs drop to normal, you probably have a sticking stepper motor. If, however, RPMs do not drop, you may yet be suffering an errant command output issue caused by faulty input, like TPS, engine coolant temp or intake air temp.

    Tune ECU would be very helpful here to monitor sensor parameters during symptom.

    I think I'm over-analyzing this though. The first three rules of diagnostics are 1) Check the Basics, 2) Check the Basics, and 3) Please Check the Fucking Basics, and I believe you have a much simpler chain reaction going on. TPS is reporting part-throttle to ECM on closed-throttle decel due to new return cable preventing full closure. I'd be looking at that VERY closely.
    No Matter Where You Are, There You Go!

  14. #14
    apriliaforum expert Robert Borchert's Avatar
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    Motech, so true. I've had schematics splayed over the bench, pages of data captures, only to discover that the intake boot is missing a clamp.

    I discovered that, with the airbox lid removed, a 1960s vintage "super ball" makes a handy stepper intake stopper. The IAC's hoses are gihugic (large) beasts, and if the hoses are original, the spring clamps have a really hard time squeezing those brittle hoses.

    All it takes is a bump, or shift in position, and you have an intake leak. Especially when moving things around to access the throttle cables.

    Bob

  15. #15
    apriliaforum expert Motech's Avatar
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    Borchet makes an excellent point. With airbox lid removed, blocking off stepper ports inside with fingers or tape (or a super ball, whatever) while idling is quicker and cleaner than trying to plug hoses and ports. If RPM drops dramatically, stepper is too far open, proceed with tap-test and plate inspection.
    No Matter Where You Are, There You Go!

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