SK5 high idle/malfunctioning STV valves after throttle cable adjustment??

[Barney626]

Hi all,

Went about adjusting the throttle cables at the throttle body end today as my top adjusters were getting to the end of travel.

Had the bike running with the airbox off to check the cables and all was good, even checked the throttle body sync and was dead on.

Put everything back together and started the bike to have it idle at over 4k rpm??? Tried turning the idle adjuster (Both ways) with no effect (even unscrewed the adjuster itself from the housing). Figured the throttle cables were too tight so pulled everything up again, loosened the cables and it still idles at over 4k.

I also noticed the STV butterfly valves move to full open but do not go half closed again when the kill switch is turned on. The manually controlled butterfly valves (lower set) appeared to be fully closed.

Tried testing the STV sensor (one above TPS) and it appears to be working (4ish volts at max open, 0.8v at closed).

The servo itself moves the valves with seemingly no issue, each time closing the valves manually by turning the nut on the servo gently it opens to fully open again. Each time it gets to the open position it seems to try and keep opening, vibrating a bit while doing so, for a few seconds then gives up.

Put the bike in dealer mode and was getting C28 and very occasionally C21.

Anyone got any ideas what I could try next? I cant see how adjusting throttle cables could break the whole servo unit and it appears to be functioning to some degree...
Having a quick look on ebay I can see a set of throttle bodies for '2005' and '2006' models, are there any differences between the two?

[Adam Ef]

You didn't nudge the Throttle Position Sensor when you had it apart did you?

[Barney626]

Just checked and its where I left it, had a paint marker dab on it to make sure.

I also double checked the STV sensor and it's giving 4.36k omhs as a reading for full open. Anyone able to say whether that's too low hence the STV's trying to open further?

Also got a quick vid of the bike running with the issue, idles about 4k rpm but the STV's seem to be doing what they should (fluttering about)???
https://youtu.be/UhV3pKFZw-Y

[Barney626]

So quick update,
Decided to disconnect the battery for an hour to reset all the electricals. Reconnected it and the servo worked properly (full open then half close) with no errors shown in dealer mode. Started the bike but it still idles at 2.5k rpm with the idle screw fully undone (anti-clockwise).

If I held the throttle tube closed it dropped down to 1.5k. The throttle cables have a good amount of free play in them at the moment.

Let the bike warm up and the rpms started dropping so screwed the idle screw in and now it's idling at 1.4k rpm like it should.

So for some reason when the bike is cold it massively over-revs, could it be related to the fast-idle system?

BTW, the TPS is correctly adjusted as I checked it in dealer mode.

[Craig380]

Probably is the fast idle screw. Don't mess around measuring the voltage from the STV sensor, just do it by the revcounter. If you measure the voltage, all you're doing is aiming for a target voltage which should give you 2,000 to 2,400 rpm on the tacho from a cold start, so just aim for the target rpm!

On the K3 to K6 bikes the fast idle screw is VERY sensitive, literally 30 degrees of rotation either way will make a big difference. I used to use a pair of very long-nosed pliers to adjust it on my old K6.

[Barney626]

So a bit more fiddling this morning and the bike appears to be behaving.

Went out for a ride and at high throttle/speed the bike very occasionally gets an FI light and clearly the fast idle is turned on. Ended up just turning the bike off while still rolling and starting it again which made the FI light go and the revs behave.

I remember reading another thread with similar symptoms but cant find it again...

[glang]

Can you ride it in dealer mode to see what code is coming up? Note C28 is not the secondary valve position but a fault with the actuator itself. It also operates the fast idle and could be down to a connection or a problem with the actuator electric motor. In the latter case there are tests in the manual to check its condition....

[Craig380]

Try giving all the linkages for the STVs a good hose with GT85 or a similar light teflon lube spray. They can get dirty and sticky with accumulated crud. Also give the nut on the front of the actuator motor a hose down, as road much can get on the shaft there and make it sticky too.

[Barney626]

So had a bit more of a play today. Unfortunately havent had a chance to ride while in dealer mode but honestly I know exactly which code it'll be showing because the symptoms are always the same.

I've found the bike runs normally until I go over a certain speed at full chat (Hypothetically tested in mexico at about 110mph or above)
Bike then gives a FI light and idles at 4k RPM but doesnt seem to be down on power.

Obviously the STV's have been set fully open, which sets the fast idle cam to max rev state and the servo stops working.

Turning the bike off/on again fixes this.

I'm wondering whether the STV sensor isn't adjusted correctly so at the full open position there's a disagreement with the STV position, hence why it only appears at high speed as otherwise the STV's don't open all the way.

Have found a couple of other threads with exactly the same symptoms but none of them posted solutions.

Unfortunately I don't have time to be swapping throttle bodies over at the moment so unless someone suggests an easy fix I'll just be living with it (very rare I go the speed required to trigger the issue) and will have a poke around at a later date.

PS. linkages are free moving and not binding at all, sprayed them anyway earlier on as it cant hurt

[glang]

That's what I had on mine many moons ago (see my FI light thread) as the fault would come up after holding full throttle for a few seconds. Turned out STV position sensor needed adjusting to give the correct reading at full opening....