Stumped - and frustrated - by high idle speed

[macx]

Have had my 04 since mid summer of last year, 08.

Have done complete tuneup - rocker end play, valve lash,
plugs, syncro'd the TB's, checked the TPS setting, everything's
set spot on and the bike runs very nicely, strong and with
little vibration.

But I can't get the idle down under 1600 no matter what.

Today I went thru it for about the 4th time -
I have free play in both throttle cables at idle
The TB's sync just about perfect at idle at the spec'd 1-1/2 turns of the brass screws.
I tried turning the screws 1/2 turn in and then 1/2 turn out from the 1-1/2 baseline with
no effect on idle speed.
I even backed off the throttle stop screws so they're not even touching the throttle
stops and, even though I have plenty slack in both throttle cables, the darn thing still
idles at 1600. Strangely, that did temporarily lower the idle speed to about 1100 but
then it shortly returned to that 1600 idle speed.

Got me stumped and thoroughly frustrated. Worst thing is in hot weather at stop lites,
of course the engine heats up faster at the higher idle.

Any ideas on what the cause might be and how to get that idle down where it belongs?

Do I need to remove the brass screws & clean out the orifices and clean the screws?
That's the only thing I can remember reading that I can imagine might have an effect
that I haven't tried yet.

The high idle for cold start seems to work as it should - it holds the idle faster until
I release it. Is there maybe some kind of adjustment there? But that's an electronic
versus a manual fast idle, or choke, function, isn't it, so there's nothing in the way of
hardware to adjust?

Thanks!!

[harveyrawn]

My relatively uninformed suggestion is to turn the brass screws further in (all the way?) and then back them out slowly to see the results.

[Phang]

My guess, air leakage somewhere between the cylinder heads and the throttle bodies (butterfly valve).

Any chance you left the vacuum ports open after your throttle sync?

[Sunbeemer]

I think Phang is right, there is some air leaking into the intake manifold and the Motronic is adding enough fuel to keep the O2 sensor happy causing your high idle...and it's probably not leaking past the Big Brass Screws, but you can remove them and replace their o-rings if you find that it is. Try squirting some WD-40 around them and the intake runner tube seals and around the throttle shaft passages on the sides of the throttle bodies to see if it changes rpms at idle... You might find a leak.

BTW, the "choke" is really just a mechanical throttle cable lift, not electronic.

[macx]

Had the twin max hooked up during the time I was working with it, so nope, those ports weren't open.
And it didn't change when I removed them and reconnected thehoses.

I checked the clamps on the TB's, tight. One other thing I will also check is the
TB flanges at the heads - had one off when I did the left cam chain tensioner so
know it's tight from when I reinstalled it, but never have checked the other one.

If that choke is a mechanical lift, maybe there's something out of adjustment there.
But what does it lift? Like I said, there's sufficient slack in the cables at idle.

I think I'll also take a closer look at those brass screws and the o-rings. And try squirting
some WD or something around the throttle shafts etc to see if it affects the idle.
Gotta be something!

That extra air might just be something - like I said, when I backed off the manual throttle
stop screws, that did lower the idle for a short time, but then it came right back up -
Thanks for that idea.

[CycleRob]

macx,

It has to be a vacuum leak. Prolly in the TB vacuum hoses that go to the tee fitting, then to the solenoid valve. Pull both hoses off the TB spigot pipes and plug one hose while applying a vacuum to the other one. With the bike off, it should hold the vacuum. If it leaks, there's the problem. It can be a cracked/split hose from the tee fitting to the solenoid valve. There's 3 weaknesses in that plastic tee fitting . . . . each pipe. If any one of the 3 breaks or cracks, it'll suck enough air to give you the high idle.

Another rare possibility is a bad or disconnected oil temp sending unit. It's failure can cause the Motronic to advance the timing. You may even be in "limp" mode.

Backing off the throttle stop screws also corrupts the TPS idle millivolts setting, but you knew that.

.

[bikermeow]

I would check the throttle position sensor, item 2:



Don't think it is defective, but probably the position has to be adjusted.

Cheers

[macx]

Had already checked the tps before I even started, and now I'm sure I'll have to adjust it.
I'm used to those things - got one on my EFI hot rod. :-)

And, yup, knew about the throttle stop screws, undertook that when I had exhausted the other
possibilities I could think of. Oh, well, nothing like starting from scratch! My trusty little 8mm
end wrench and my old carb idle screw flexible screwdriver tool will take care of them.

Now, about the little vac hoses - I've never really seen where they go or what they
hook up to - I suppose getting to that T you're talking about is a major undertaking?
I'll check that out - learn something every day - in spite of myself. But first gonna
squirt the TB connections and throttle shafts to see if there's a problem there.
But, nooo, won't be THAT easy! But I'd sure like to know where it SAYS it can never
be easy!

Plastic T, huh? Another plastic wonder like the QD's? Wow, they probly saved $.050 there!

Hmm, temp sensor. I'll see if it's disconnected, but if it was in limp mode, would it run strong
off idle? I've got a digital vm, what should it put out? Is it an on or off thing, or graduated signal?

Looks like cold rain for a couple days, got my tender plugged in, gonna sit this out and see
if I can get over the creeping crud and hope it'll warm up a little after the storms. Was
downright shameful, 55F this afternoon when I went to work with a forecast low of 50 and
no rain, but didn't ride, even tho only 6 miles. Getting sick and tired of being so sick and tired -
over a week now. I've gotten over it I'll bet 4 times, then get back into the wind at work at nite
and right back at it.

Thanks for all the thoughtful advice! I'll post what I find. Maybe someone else can benefit.

[boxermania]

macx

One easy way to find out if the problem lies with the lines out of the bottom of the TB's is to remove such and plug the holes to see if the idle improves. The lines from both TB's come to a T and then proceed to a small solenoid attached to the frame, on the right side and under the seat.

Regarding the TPS, the idle voltage range is from .355 to .410 VDC, most of the time it is set mid range right arount .380 VDC. (this is measured with a DVM from the last wire on the plug, towards the back of the bike and ground while moving the TPS). Of course this assumes that you have both butterflies resting at the mechanical stop and with the same opening angle. But I think you know that from your prior experience.

Let us know how you make out.

[macx]

macx

The lines from both TB's come to a T and then proceed to a small solenoid attached to the frame, on the right side and under the seat. That's what I needed to know, thanks

Regarding the TPS, the idle voltage range is from .355 to .410 VDC, most of the time it is set mid range right arount .380 VDC. Yup, mine was at .37 before. I've read that upping that a little closer to .400 at idle enriches the mix just a slight bit but you have to be careful not to go over the upper value or you have to reset, I know on my hot rod there are folks that feel it's important to get it really close to a specific value, incl the very popular & leading mfg of aftermarket mass air meters, altho the oem mfg of course just has an acceptable range - so of course being rather picky I set it precisely and it does run really nice

.

Massive rain today and cold, so gonna stay domestic for a day or 2, gotta get a little nicer sooner or later!

[macx]

Well, may have finally come to the end of the search for an answer.

To summarize:
full tuneup incl TB synch at idle and at cruise rpm
specified throttle cable free play at closed throttle
"choke" wasn't holding throttle cables open
idle wouldn't settle down below 1400+

Per some appreciated advice, checked the vacuum in the hoses
under the TB and thru that T - held vacuum fine

sprayed accelerant around TB's - shafts etc - and their connections to the intake ports -
no engine speed up at all. Also checked the attaching bolts and the clamps, all tight.

finally this afternoon had a chance to re-check the manual throttle stop screws,
the ones we're not supposed to mess with.

I had loosened them before when I had run out of other ideas, but apparently not enuf
on the left side, which today I backed out till it wasn't touching the stop. The right side screw
hadn't been touching the stop.

Today I set the cruise on about 2200 and let the engine warm up a little while, then
backed the cruise down so the engine was running at 1100 steadily. This was after I
checked the throttle stop screws and found the left one was still touching the throttle stop -
this was after I had added more slack to the throttle cables just to make sure and then
synchro'd the TB's at 2500.

I then carefully screwed the throttle stop screws in very slowly, one at a time, until
the engine sound changed as if it were just starting to increase rpm, or trying to on
the side I was adjusting. Then backed them off just to the point that change hadn't
quite started to happen yet. Didn't have time to put the twin max on, had to get ready
for work, but when I released the cruise control VOILA!! The engine stayed running
at a steady and smooth 1100 rpm!! Having eliminated the other possible causes, that
sure seems to have been the problem all along. I don't know if the factory had goofed
the setting, or a previous owner had messed with it, althought the blue loctite was still
on both throttle stop screws.

Now that I seem to have the basic problem solved, I'll of course have to lock down the
throttle stop screws - with the twin max hooked to try to get them as well sync'd as possible
and with the idle at 1100, then adjust the throttle cables for the proper free play,
then recheck the sync on the throttle cables at i.e. 2500 rpm or so, then idle it down and
fine tune the sync at idle with the brass screws, then check (and probly reset) the tps.

A lot of darn work and time to correct that high idle!!

[Sunbeemer]

then adjust the throttle cables for the proper free play,
then recheck the sync on the throttle cables at i.e. 2500 rpm or so, then idle it down and
fine tune the sync at idle with the brass screws, then check (and probly reset) the tps.

My understanding of the throttle stop screws is that they are set by the factory to adjust the air control plate to be perpendicular to the axis of the throttle body, which prevents them from being damaged. The idle is then adjusted using the big brass air-bypass screws, and once that is set, then the throttle cables are adjusted for equal pull. So, if you adjust the cables first and then go back to adjust the brass air-bypass screws, it would probably throw off the cable adjustment. They way I do it (note I've never had to deal with idle screw adjustments) is adjust the brass bypass screws at idle first, and then adjust the throttle cables at 3000-4000 rpm under load. This make it smooth!

If you reset the TPS (I believe it should read ~400mv at idle), then be sure to reset the Motronic by removing fuse #5 for 30 seconds, then replace it and turn on the ignition without starting the engine and crank the throttle wide open a couple times before starting the engine. This calibrates the Motronic to the new TPS range.

Glad you got your idle back!