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Discussion Starter · #1 · (Edited)
Rough idle and poor slow speed running can often be caused by a faulty idle air supply circuit.

With the throttle in the released/closed position, the throttle butterflies are fully closed and air supply to the engine is controlled by the idle actuator, which is sited at the base of the air box. Air is drawn from the air box, past the idle actuator valve, and into the throttle bodies just below the butterflies. If you turn the ignition on and, after the self test, turn it off again, you will hear the idle actuator motor cycle to its rest position (a slight grrr sound for a second or two).

The idle actuator is a valve that progressively opens/closes via a stepper motor controlled by the engine control unit. From a cold start, the actuator will be at a high stepper motor setting, and will progressively close as the engine warms up, settling at around 44 +/- 3 steps to maintain the specified idle rpm. The attached graph shows the stepper motor position and engine temperature from a cold start. Once warmed up, the stepper motor setting settles at a fixed position.

If this air flow is interrupted in any way - eg by a kinked air hose or dirty/faulty idle actuator, then poor idle or rough/abrupt low throttle running will result, perhaps even stalling. The idle circuit seems to lose significant influence above around 2000 rpm and at high throttle openings.

See also further info on the idle actuator itself:
http://f800riders.org/forum/showthread.php/73969-800-Twin-Idle-Air-Controller-Failure

Early in my ownership, my bike seemed to be a bit lumpy at idle and on investigation I found that one of the air hoses showed signs of being kinked. (Later models have hoses with a pre-formed shape to avoid this, although there has been at least one case where the dealer mechanic retro-fitted these upside down, resulting in severe kinking.) Not having new hoses at hand, I wound some guides from light wire, fed the tubes through, bent them into the required shape, and refitted, taking care to fit the tubes into their locator clips on the bottom of the air box (top of the first picture). I also took the opportunity to remove the idle actuator and wipe down the valve with a bit of carburettor cleaner on a rag (not worrying about the staining). Others have cut the air tube and put in a V/U junction to achieve a similar result.

Reassembly is a bit tricky after doing this as there is less flexibility in the hose, but the results were dramatic. I now have smoother idling and low speed running, as well as improved economy. On my normal outer suburban commute (speeds up to 100 km/h and average ~53 km/h) consumption has dropped from 4.2 litres/100 km to 3.9.

Experience has also shown that a dirty idle actuator plunger and bore can cause erratic idling and stalling, and so it is worth cleaning each time the air box is off (e.g. at major service) using carburettor cleaner spray (spray onto a cloth then wipe, to avoid getting solvents in the stepper motor). The pictures below show the actuator disassembled as far as you can - it isn't necessary to do this, but if you want to:
- with the battery and actuator re-connected, turn the key on then off
- when the plunger cycles and is trying to regress towards the actuator motor, hold it to resist its movement
- repeat until the plunger works its way out far enough to unscrew completely
Re-assembly is the reverse of the above, taking care to ensure the plunger's rest position is close to the actuator body; otherwise you may cause damage when you re-attach the actuator to the air box. It's also necessary to align the profile of the plunger shaft with the guide aperture. The metal sliding section has two flats on it that fit into the actuator motor assembly to stop it rotating (and hence allow the worm drive to work). I used some light grease on the thread and sliding section of the shaft. Take care to ensure you re-use the same grooves in the air-box thread (turn backwards until you feel a click, then it should easily screw in); otherwise you might eventually strip the thread. If the plunger is loose on the actuation shaft, then the whole assembly will need to be replaced, I would expect.

If the idle actuator fails completely, the bike is unlikely to idle and run properly at rpm lower than 2000. An emergency fix is to remove the slack from the throttle cable, and then some, thereby allowing air to be drawn past the slightly opened throttle butterflies instead of via the idle actuator circuit. I haven't actually tried this, but if you start then warm the engine at moderate revs by holding the throttle open, you may then be able to get the bike to idle reliably somewhere around 2000 rpm. Not ideal, and I expect a pain to ride, but at least it should get you home. I suspect the bike will adapt to the new 'zero position' so it isn't a long term fix by any means.

The GS911 has a recalibration routine that runs the idle actuator through a full closed-open cycle three times to re-establish the engine management computer's understanding of limits of movement. This is important I understand for boxer engines (they have an idle actuator for each cylinder) to ensure good left-right synchronisation and therefore even idle. I'm not convinced it is important for the F800 though - the actuator seems to go through this cycle when you turn the ignition off (that grrr sound, if you do it when the engine is not running); boxer engines may also do this, but I have no experience with them. In fact with the air inlet horn and filter removed, you can watch the actuator in action if you turn the ignition on, then turn it off again. When turned off, the actuator moves fully closed, the stepper motor continues to run for five more steps or so, then it fully opens (in my case, to 189 steps open). When you turn the ignition on, the stepper moves the valve to the start position (which I assume is temperature dependent - in my test, to 100 steps with 15 deg C ambient temperature).

A similar cutting out symptom can also be experienced if the throttle position sensor (TPS) goes out of calibration. The sensor is a potentiometer at the end of the throttle butterfly shaft and, when calibrated, the ECU knows the voltage for 0% and for 100% throttle opening, interpolating in between for any other throttle opening. If the calibration is out, you can imagine the ECU applying inappropriate fuel mapping for the actual throttle opening, and then trying to compensate for being too rich or lean, plus (potentially) incorrect idle actuator settings. The GS911 has a function for resetting adaptive values, which includes the throttle position sensor and the gear position sensor. If nothing else, disconnect the TPS connector, clean with a spray of contact cleaner, and reconnect.

Other posts on this forum advise that to reset the throttle position sensor, turn the key to ON, turn the throttle to fully open, hold for three seconds, then return to closed for three seconds; repeat a four times, then turn the key off for 15 seconds. I haven't tried this technique.

For those new to getting to the idle actuator:
  • remove seat
  • remove both mirrors
  • remove fairing top cover ('faux tank')
  • remove each top side fairing panel (lower panels can remain in place)
  • disconnect negative then positive terminal of battery; remove top clamp and take out battery
  • disconnect the electrical quick-connectors (intake temperature sensor and secondary air system valve) around the top of the airbox (the big black thing) and release clipped wiring
  • release secondary air system hose quick-connector (at top right - squeeze sides)
  • remove intake horn and air filter by lifting out the two clips on either side
  • release the bottom mount of the starter relay (left front) by rotating the relay anti-clockwise; then ease upwards to release the top mount
  • remove the four air box mounting bolts, taking care to collect any of the loose washers (some might stick to the mounting rubbers)
  • lift the air box a little and remove the two hoses from the idle actuator (may need a little twisting to release their grip)
  • detach the idle actuator electrical connector (I think it needs a small screwdriver to release the locking tab, or is it a squeeze one - can't remember)
  • disconnect the crankcase breather pipe at the front of the airbox while squeezing the pipe clamp with suitable pliers
  • lift off the airbox
  • cover the throttle valve assembly to guard against anything dropping in
  • remove the idle actuator from the airbox by removing the two screws

Reassembly is the reverse, taking care to ensure:
  • the idle actuator screws are returned to their original threads rather than cut a new thread (turn anticlockwise until you feel a click, then screw in)
  • idle air hoses are correctly routed and in their locators at the base of the airbox
 

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Hi there,

My bike was idling poorly so I decided to try and fix the kinked hoses as you described. I didnt have springs to stop the hoses from kinking so i tried to use a thicker hose pushed over the standard ones. Put it all back together and OOPS it cant even idle!!!

Pull it all apart again, scratch my head for 5 minutes, then decide to re-route the hoses around the throttle bodies instead of between them (as seen in your last pic). Put it back together...and SUCCESS idles like a inline 4 (Ok not quite but its perfect now). Going around the throttle bodies prevents the hoses from kinking when you push the air filter back down into place, EASY FIX!!!
 

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Strange idle when dropping gears

Hi guys! Just bought my 07' 800 ST about a month ago and and loving. Everything, except that she already threw me against the back of a BMW 520D lol. When was dropping gears to stop at a stoplight, dropped to 2nd gear and when I released the clutch she started accelerating and BANG (yes, I have cut the throttle all the way). Minor damage, luckily only a broken front fender. The same thing happened to me the very next day, but I was already on my toes with the situation, so nothing bad happened. Have you guys ever experienced that strange idle increase?

Other thing. Mokkybear have you ever noticed that the bike steers better to the right than to the left? I'm a newbie but now I've been ridding for a few weeks and I'm starting to get to know the bike. I noticed she turns smooth to the right, but to the left she's always like trying to fight me to stand up. I tried to ride a bit with no hands and she starts turning slightly to the right. May this has something to do with it... I noticed because on my previous bike I turned a lot better to the left (it's my "natural" turning side), so stated the rear tyre. On the 800 ST the tyre states the opposite, that I'm leaning more on the right hand side. Weird... I find it harder to turn to the left.

As last, another thing. This already happened to me 3 times. Dropping gears to stop and when I fully press the clutch the engines cuts dead. Pffff lights off. Sometimes, already happened twice, I start the beemer on the stand and after a few seconds she cuts dead too. Maybe a software problem, something to do with the V8 software you guys spoke about?

Thank you guys, I'm really starting to get freaked out with all this stuff.

Ride Safe,

DirtyHarry
 
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Wish to thank Mokkybear for the insight. Replaced the air hoses and cleaned the actuator as outlined. The results were great. Used hoses with a thicker wall but the same i.d.. Hope this helps prevent the kink in the hose that causes the problem.
 

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WAW, nice post. I had the same problem, F800S 2006, had this problem for two years, but at bmw service seems normal, that the idle is not smooth. They told me that it becouse of Leovince exhaust?!? It could be, a thougt. Last year, the idling was even worst every month, and on my service at 50kkm, the mechanic told me, this was still normal. The rpm at idling went from 1.100 to 1.500 randomly, and sometimes when opening gas, the engine didn't respond in the moment, but loose some rpm and then raise it. But at least it didn't die. Maybe 5times per year, becouse i get used to it and beeing gently with throtle. Two weeks ago, i started the engine after 2 month resting, and when cold it does idling, not smooth, but good enough, and when getting hotter it dies suddendly when relesing throttle. But now i see, that this what you describe in your post could be the problem i have for some time! Thank you for great post and pictures. Now i see where to look for resolving my problem. Shame on bmw mechanics, they really suck, at least in slovenia! This should be replaced years ago, when it was still under warranty...now what can i do. i asked them every time i went there for regular service, to check and change the recals and possible problems this f800 2006 series has, but they never did. :( The only thing, that is still hanging me to not sold my f800 is becouse i like it, and becouse of this great forum and community. TNX.
 

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Discussion Starter · #8 ·
The hoses exit the bottom of the air box, and so it is necessary to remove it. (You can just see the hoses where they attach to the idle actuator by looking through the gap just above the frame.)

Thus you need to remove seat, air box cover panel, mirrors, upper fairing panels, battery, then air box. To lift the air box, you need to ease the air hoses off the idle actuator.

The fourth picture in my original post shows evidence of flattening of the hose where it bends most sharply.
 
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Hello Mokkybear.

I am sure this is the problem I am having. I suspect BMW NOG moved or adjusted something in that region not aware of the kinking when hot. The bike will die pretty much to cue before engaging 2 gear pulling in the clutch but only after a period of fast running say 30 mins.

Not sure I can remove all these bits though. I bought a Haynes workshop manual at the weekend and it doesn't mention breather hoses or Air Box at all. Is an air box a radiator. It's the terminology that is different.

Go on have a good laugh.

If so then the radiator cowel is the air box cover panel.
 

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Discussion Starter · #10 ·
The air box sits above the engine - the big black plastic thing that holds the air filter and snorkel, with two holes in the bottom that connect to the engine inlets, plus a few other sensor connectors and hoses. The battery is mounted in the front part of it. See page 4-3 of your Haynes manual - looks a bit complicated when described on paper but is quite intuitive really when you have a look at the real thing.
 
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Hello Mokkybear.

I am sure this is the problem I am having. I suspect BMW NOG moved or adjusted something in that region not aware of the kinking when hot. The bike will die pretty much to cue before engaging 2 gear pulling in the clutch but only after a period of fast running say 30 mins.

Not sure I can remove all these bits though. I bought a Haynes workshop manual at the weekend and it doesn't mention breather hoses or Air Box at all. Is an air box a radiator. It's the terminology that is different.

Go on have a good laugh.

If so then the radiator cowel is the air box cover panel.
Hi Streety. Happy to have a look if you fance a longish ride over my way one day.
As Mokkybear says it's pretty easy to do.
Take the pained panels off and you will se the big black airbox right where a fuel tank would be normally. You can then just about see the two black hoses if you look.
The airbox can be unbolted (battery has to come off as two bolts are under it) and two bolts at the back one each side. A few wires and plugs and the breather pipe and the black box will pull off.
You can see some of it if you look at my old valve check video
 
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Duff Air hoses

Managed to pluck up the courage to have a look at this.

As you said it easier than it looks. 22 fairing screws, assorted clips and connectors. The air filter was lovely and clean. The air box has a bit of resistance getting them off the throttle bodies and low and behold the right hand side hose was kinked.

I suspect that North Oxford did not feed the hoses through the guides at the top of the air box when last servicing. The hoses were coming down cock eyed and the right one pushed up against the ECU (I think) had a definate kink.

I fashioned a piece of Garden wire (as per instructions) and fed them over the hoses and replaced everything. It started so fingers crossed it will fix the problem.

I was actaully quite impressed how beatifully engineered it all was.

I am buzzing. Its my first mechanical fix. Now to strip down the engine...only kidding.

Thanks again everyone.

Hey Pat, I still fancy coming down to visit. PM me a perhaps we can put a date in the diary.
 

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Hum... gotta take a look at this. The thing is my bike is still under warranty from the dealer I bought it from, I don't know if I should try "mechanics" on her. But... she keeps dying on me. Specially as streety said when pressing the clutch. Yesterday it happened when downshifting to enter a curve... Spooky!
I really gotta take a look at this issue if I want to maintain the rubber side down :(.
Thank you guys for the wonderful knowledge base this forum is.

Ride safe and try to keep the shinny side up,

DirtyHarry
 

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Discussion Starter · #16 ·
Good work Streety - another victory for the home mechanic! [clap] I'm sure there are BMW dealership mechanics who are not aware of this issue and you've sorted it out for free.

Fundamentally I think the F800 engine is a fine design, but especially given that it's tuned for economy, everything has to be working well together for the bike to run smoothly and as designed. Restrict air flow through one or both of the idle circuits and the fuelling components aren't working in harmony - hence a lack of smoothness at low throttle, and unreliable idle.
 

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Mokkybear, Good on Ya! The simple cheap-o solutions (wire wound strain reliefs) are the best ones. Fortunately, my 2009 model has the thick walled hoses with preformed bends.

The solenoid valve in-line with the hoses connected to the center of the valve cover is the air injection cut-off backfire valve. It does not deal with crankcase vapors. The valve cover location for the passageways are just an easier way to house the necessary check valves and connect passageways to the area near each cylinder's exhaust valves. Those vent hoses deliver filtered air from the airbox (not the crankcase) thru 2 one way reed check valves to the exhaust ports from each cylinder, to burn any remaining unburned fuel inside the header pipe. The solenoid backfire valve closes off that airflow to prevent backfiring on closed throttle deceleration, when it is most likely to occur. It is open at idle and any "on-throttle", but closes on high vacuum closed throttle engine decel.

Disconnect the backfire vent hose from the airbox opening, run the engine and wack the throttle open/shut and you'll hear the gurgling sounds roar then stop when the crankshaft RPM's are decelerating. You can even shoot a couple bursts of WD-40 into the hose while it's running to clean/lube the system, although the exhaust smoke may embarrassingly "crop dust" your vicinity if the glowing catalyst inside the muffler doesn't consume all of it. The gurgling sound is the air being dynamically pumped thru the vibrating reed check valves, between the exhaust pulses. That same system goes back to the early/mid 1970's as our first attempts at exhaust emission control. Cars/trucks at the time used an engine driven air pump to move the air, but it was later discovered that thin SS reeds in a properly designed check valve could take advantage of the exhaust pulses to create the required airflow without any electrical or mechanical energy input. An energy efficient freebie air pump.

It would be a good idea to incorporate a WD-40 internal cleaning/lubing of the 2 solenoid valves (Canister vent and air injection backfire) plus the idle control stepper motor at every 12K service. Remove and take them apart to thoroughly do the job. The 2 thin steel reed valves housed in the valve cover also get gunked/carboned up from normal usage and can/will negatively affect the idle if exhaust gases go backward into the airbox. That may be what is causing unexplained, error codeless, erratic idling and stalling on high mileage bikes.

BTW, the WD-40 will not harm any rubber/plastic valve parts -and- is totally harmless if/when any residual or excess WD-40 is sucked into the TB's or exhaust ports when the engine runs. Great stuff it is.
 

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Thank you Mokkybear!!! No Really!!! I was totally vexed when my st came back from a 60k valve adjustment / fuel injector clean and was idling terribly. Not wanting to wait from early June to mid July (their next appointment time) I looked up "rough cold idle" on the search engine and found you excellent article. I did the suggested wire wrapping trick and it completely fixed the problem. You are the Man. I mean you are the John Motherf*%#king Shaft of the f800 world. Thank you!!!
 
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