CB1100 Idle speed instability problem

[Cormanus]

Dave, sadly there’s no way I can answer the question you pose, but I did want to tell you I’m full of admiration for your incredible persistence chasing down a solution to this problem.

[Dude_imp]

The only time i have idle issues is in stop and go traffic for > 1 hr, idle drops down to 500rpm sometimes, hasnt died on me yet though. Otherwise everything is on point.

[max]

Hi Dave, big learning curve by the sound of it, however you have made the journey into the forest, the way out should be easyer.

Q1; was the iacv disconnected when you removed it? picking it was connected.
q2; now that they are both out is there a difference in binding the threaded part i.o.w. does the old one run freely?

a1; position of the piston inside; it has worked fine before all the trouble started so unless the ecm has slowly dribbled out of position ( stuck during part of the travel and still counted the same amount of steps ) i expect it to be correct.

"There is something potentially wrong with the way the valve came out though. I expected the valve to have been positioned all the way to its "as-installed" location, which is the valve rotated clockwise the full length of its travel on the threaded shaft, (this is how the FSM instructs you to install the valve) but instead, it was about 1/3 of what I "estimate" to be its full travel in the opposite direction."

As far as i can work it out it chases a moving setpoint depending on air and engine temperatures so it should have a tendency to "shuffle"along the working part of the cylinder and resets to a pre- determined position every time the engine is started from cold.
In other words it automatically finds it's own spot.

The concern i had was if the piston was initially mounted too far into the barrel ( not wound back ) and the thread was compressed against the end of the barrel where it has a minimal amount of threads on initialisation.

I think the real answer is that you would need an obd2 tool to tell exactly where the piston is at any time, however we know that it is not in the target position if the engine idles badly, so you can reliably guess when it is too far open or closed.
( if you can see the shadow of a tree you know the tree is there otherwise what makes the shadow?)

a 2; if the iacv was connected and the bike idled ok prior to being switched off the iacv was indeed in the correct operating position for a warmed up engine, well done Dave.

Could it be that the valve was on an angle in the barrel? ( Minor scuff marks at the very end of the tip of the piston )
Can we have a look at pictures of both iacv's prior to mounting the new one?

[the Ferret]

The only time i have idle issues is in stop and go traffic for > 1 hr, idle drops down to 500rpm sometimes, hasnt died on me yet though. Otherwise everything is on point.

I can't imagine living anyplace where I would be in stop and go traffic for more than an hour. What a nightmare that must be.

[dave]

Dave, sadly there’s no way I can answer the question you pose, but I did want to tell you I’m full of admiration for your incredible persistence chasing down a solution to this problem.

Hi Cormanus, thank you very much. I have to thank all the great people on this forum who have encouraged and supported me the whole way. The job is only half way done now, and I am praying that the new IACV will cure this idle problem.
Q1; was the iacv disconnected when you removed it? picking it was connected.

It was disconnected for the last 50 miles I rode the bike, with slow idle on start-up, and perfect idle with the engine warmed up.

q2; now that they are both out is there a difference in binding the threaded part i.o.w. does the old one run freely?

No. Both valves thread very smoothly the full range of travel on the threaded shaft.

a1; position of the piston inside; it has worked fine before all the trouble started so unless the ecm has slowly dribbled out of position ( stuck during part of the travel and still counted the same amount of steps ) i expect it to be correct.

This is a possibility. I posted a while back that the sound I heard when I first turned the key on became noticeably louder on one occasion. It could have been the IACV noise, but then again it may have been the fuel pump.

As far as i can work it out it chases a moving setpoint depending on air and engine temperatures so it should have a tendency to "shuffle"along the working part of the cylinder and resets to a pre- determined position every time the engine is started from cold.
In other words it automatically finds it's own spot.

Question: If it finds its own spot, can it automatically compensate if it is installed incorrectly - ie, if the valve is not threaded completely to the bottom of the threads on installation?

The concern i had was if the piston was initially mounted too far into the barrel ( not wound back ) and the thread was compressed against the end of the barrel where it has a minimal amount of threads on initialisation.

I think the real answer is that you would need an obd2 tool to tell exactly where the piston is at any time, however we know that it is not in the target position if the engine idles badly, so you can reliably guess when it is too far open or closed.
( if you can see the shadow of a tree you know the tree is there otherwise what makes the shadow?)

a 2; if the iacv was connected and the bike idled ok prior to being switched off the iacv was indeed in the correct operating position for a warmed up engine, well done Dave.

The bike idled fine when warned-up, with the IACV disconnected (which it was for about the last 50 miles, and three around town trips). Do you think it's possible that the valve somehow moved (vibration?) during the 50 miles I traveled with it disconnected? I am guessing that it would not.

Could it be that the valve was on an angle in the barrel? ( Minor scuff marks at the very end of the tip of the piston )

I don't believe so. There is no visible indication of any kind f damage or scuff marks, and the valve removed effortlessly from the cylinder, indicating no binding at all.


Can we have a look at pictures of both iacv's prior to mounting the new one?
[/quote]
I will provide pictures, but you won't see any difference between the two valves.

My next step will be to reinstall the battery and test both old and new IACVs side-by-side. I hope they will work - I have disconnected many wires that I don't know if this will have any effect. I did inspect the new IACV prior to any disassembly and it appeared to function properly (to the best of my knowledge, anyway). I can only compare the old to the new to see if there is a difference.

[Dude_imp]

The only time i have idle issues is in stop and go traffic for > 1 hr, idle drops down to 500rpm sometimes, hasnt died on me yet though. Otherwise everything is on point.

I can't imagine living anyplace where I would be in stop and go traffic for more than an hour. What a nightmare that must be.

I can't imagine living anyplace where I would be in stop and go traffic for more than an hour. What a nightmare that must be.
Not a usual occurence thank god.

[max]

Nice going Dave, in order of appearance;
Disconnected in the running position and idling perfect for 50 miles, you stated it before but i like the sound of that!

a1; don't think it moved, which brings me to the first question; you know more about the iacv movement now, so can the shaft rotate when it is not electrically energized or is the shaft stuck or magnetically held in position ( moving but you can feel the magnetic poles hold the shaft ) when you try to rotate it?

My feeling is that the stepper motor was gradually having more difficulty in moving the shaft, reasons i can think of are;
piston not aligned with the barrel, thread binding ( i think you eliminated both of these ) pin that guides the piston too short or too long, bearings inside the stepper motor running low on lubrication, are the two stepper motors evenly strong or is one weaker? and lastly something inside the iacv motor that got in the way ( debris )

Is the piston made of plastic or metal?

can the piston unscrew completely from the shaft or is there a stop at the end and are the springs the same strength?

When you install the battery i think the iacv ( plugged in but not mounted so you can see what it is doing ) will cycle as normal, it will even do this in limp mode because it is part of the initialisation and the computer is not making a decision yet, it only sets the engine up for warm or cold start.
If you hold the piston with your fingers you can see it travel in or out ( forgot which way but it is not important for now ) .
The ecm does not know where the iacv piston is on startup, so the engineers have programmed a simple routine in the ecm by extending the travel a few steps more than required to get to one end ( either open or closed ) from there it knows the piston is at the end of travel and moves the piston in reverse----- by the amount of steps required for the operating temperature ect.----- and now the ecm knows that the piston is in the correct position to start the engine.
This always works ok on startup, every time, but something happens sometimes after some time that makes the ecm think the piston is in the right place but it dragged it's feet and is somewhere else.

I would listen to any noise that is different between old and new iacv, i am sure you have given us the clue with the different sound when it is not behaving but i cannot decode the hint for now.

If you switch on in the 30% ( warm running position in which you found it ) i think it will go to one end first and then move back some distance.

Thank you Dave.

[dave]

Is the piston made of plastic or metal?

It is not magnetic. I think it's aluminum (it's real light weight), but it is shiny in appearance. It's possible that it's a hard plastic, and I will have a closer look at this and get back with a better answer.

can the piston unscrew completely from the shaft or is there a stop at the end and are the springs the same strength?

The piston can be unthreaded from the shaft. What springs are you referring to?


The ecm does not know where the iacv piston is on startup, so the engineers have programmed a simple routine in the ecm by extending the travel a few steps more than required to get to one end ( either open or closed ) from there it knows the piston is at the end of travel and moves the piston in reverse----- by the amount of steps required for the operating temperature ect.----- and now the ecm knows that the piston is in the correct position to start the engine.

So does this mean that if the valve is not threaded down completely when it is installed (like mine was when I removed it) then the ECM will automatically compensate and send the proper signal to the motor to properly locate the valve?


I would listen to any noise that is different between old and new iacv, i am sure you have given us the clue with the different sound when it is not behaving but i cannot decode the hint for now.

I will operate both valves while holding them in my hand and report back my observations.

If you switch on in the 30% ( warm running position in which you found it ) i think it will go to one end first and then move back some distance.

So, then the fact that my valve was not threaded completely to the bottom of the threads when I removed it (the way it is supposed to be when installed) makes no difference? I was hoping that this was the root cause of my problem.

Thank you so much for your help Max. I don't think I'll be able to get back to the bike until this Saturday, but I will keep this thread updated as I progress.

[Magnus_imp]

Dave,

If you run into any trouble I'm in San Diego as well and did the IACV a while ago as you probably know. I think I remember most of it. Sounds like you have a good hand on it and are taking it slow. But if you get truly stuck I'll be around this weekend. I could bring my CB so you can compare parts/wiring locations if you get lost. Eight Five Eight Nine 6 7 5 4 Eight 0

- John

[pdedse]

Dave,

If you run into any trouble I'm in San Diego as well and did the IACV a while ago as you probably know. I think I remember most of it. Sounds like you have a good hand on it and are taking it slow. But if you get truly stuck I'll be around this weekend. I could bring my CB so you can compare parts/wiring locations if you get lost. Eight Five Eight Nine 6 7 5 4 Eight 0

- John

I have to say, knowing of this just made my day--and I'm not even Dave.