CB1100 Idle speed instability problem

[Speed_imp]

Think i know what you mean Speed, to test this you could get the engine up to temperature and idling 1050, disconnect the iacv and go for an extended ride.
With the iacv now " stuck" and not responding your symptoms should appear when slowing to an idle as per usual.

The "check engine light" will be on except when two 100 ohm resistors are connected instead of the iacv coils, and the engine will lose some power when the cel is on if i remember correctly.

Very encouraging to see that you are working all this out on your end.

With IACV disconnected I am not able to reproduce the issue, but also the engine management probably enters in Limp Mode, Open Loop and does not correct the mixture with the Oxygen Sensors. MIL light appears, idle speed is always stabilized.

MAX,
We will see how IACV works on Saturday.
I'm getting more and more curious.

Backing to :

"One possible explanation could be that the permanent magnets inside the iacv loose strength over time due to the heat"

I wonder why, therefore, a quick reload IACV which is done by turning the ignition key off and on again restores immediately proper engine speed for some time.
Since the engine and the IACV itself does not have enough time to lose high temperature.
Therefore, the magnetic properties of the IACV rotor do not change because the temperature has not changed.

I am already tired today.
I am going to sleep because I have to get up early for work tomorrow.
The good news is that tomorrow morning I will ride a motorcycle again.

Good night to all

Pawel this turned out to be a very good question

At first i thought " youre right, the iacv works fine when cycled again, nothing wrong with the magnetic rotor".

And i did not reply back, however after i woke up this morning things started to fall in place and since we could not yet find something wrong with the iacv but it had to be at fault

So i looked at what the difference is between the startup and run situation, all things were the same xept ( new spelling ) the with of the pulses, here are two screen grabs of Lord Popguns excellent video, see if you see what i see;



Now compare that with what happens when the engine is warmed up;



To me that looks like a very short pulse compared to what the iacv is designed for

That looks like they have a pulse generator running all the time and take a timeslice to drive the iacv ( turn the driver on for x amount of programmed time ) and do not take the sync of the generator in to account.
So the pulse shape sent to the driver is mutilated because the processor has it's own timing priority together with many other things it controls and slots the iacv in when it feels like.

If the pulse timing is just long enough to make the iacv work normally ( it takes time to rotate the shaft ) the designers would be happy with the result ( although it is a marginal substitute of what the pulse should be ) and put the bike in production; it works, right?

How many programmers would look at the with of the pulses and decide it is not as the stepper motor is designed for and change the timing effort from "pulses on for x amount of time " to ;
" this many steps " as it should be to make this action reliable rather than " it works ".

And if the software was changed to allow a longer set of pulses, like double the time that would solve the situation a lot i think.

Now for the second part; what would happen if we connect capacitors across the coils?

See how important your reply was? it made me think

MAX , Speed
I found out how a stepper motor works here from You.
Perhaps my statements do not make sense but ....
I don't know how many pulses the motor need to make one 360 degree turn.
I don't know how many degrees the motor moves during one pulse.
I also don't know if half of the pulse will move the rotor by half of the value (of one full pulse) or maybe nothing.
My imagination tells me that it is like this:

MAX , Speed
I found out how a stepper motor works here from You.
Perhaps my statements do not make sense but ....
I don't know how many pulses the motor need to make one 360 degree turn.
I don't know how many degrees the motor moves during one pulse.
I also don't know if half of the pulse will move the rotor by half of the value (of one full pulse) or maybe nothing.
My imagination tells me that it is like this:
In my opinion this last signal is not an issue, if it was the case the problem would be the ECU, and the valve can not move half step, only can move from one magnet to another, the position of the magnets is defining the position of every step. The last signal which is smaller in time only occurs because it just stops the pulse train there. But while engine running at idle speed I don't know why the signals are shorter, anyway it does not seem to be aproblem, the signals from Popgun's video are correct and his bike is working as designed. I am starting today with my IACV replacement!! Your case and Popgun's videos finally triggered me to replace it and leaving the diagnosis as completed. Thanks!
Finally I received the IACV valve, I will replace it as Dave suggested without removing the throttle body which is probably the more compromising operation.



Let's see if I can get it replaced today and give feedback.