RE: CB1100 Idle speed instability problem

[Lord Popgun]

Keep in mind that our IACV does not have a feedback loop. It doesn't send anything to the ECU.

[max]

Lambchops agree completely with your post except Popgun is right, no feedback is available from the iacv, ( although you could look at the rpm's and call that feedback, just how you interpretate feedback )

What happens is; whenever the bike initiates ( when you hear the fuel pump prime ) the iacv opens completely to the stop, and depending on the engine temp it then closes to supply air to idle the engine at the programmed amount.

It also activates on the clutch lever switch and the throttle and assist to prevent stalling from a standstill as programmed.

You can check this by starting the engine before the pump finishes priming, the rev's are higher and return quickly to the correct setpoint.

What i personally think happens is; the pulses are just long enough to rotate the iacv when new but as the permanent magnets inside the iacv heat up ( slow traffic ) over time they lose strength and the ability to work with the short pulses.
Something changes to deteriorate some iacv's over time and they don't respond well with small steps.
I think the software provides better shaped pulses ( more energy ) as was provided with the old software.
Noticed some half shaped pulses on the owner from spain with his research, starting with a full shaped pulse step is better then a fraction of that value.

We may never know what really happens but this is my best shot at the moment.

[SportsterDoc]

Lambchops agree completely with your post except Popgun is right, no feedback is available from the iacv, ( although you could look at the rpm's and call that feedback, just how you interpretate feedback )

What happens is; whenever the bike initiates ( when you hear the fuel pump prime ) the iacv opens completely to the stop, and depending on the engine temp it then closes to supply air to idle the engine at the programmed amount.

It also activates on the clutch lever switch and the throttle and assist to prevent stalling from a standstill as programmed.

You can check this by starting the engine before the pump finishes priming, the rev's are higher and return quickly to the correct setpoint.

What i personally think happens is; the pulses are just long enough to rotate the iacv when new but as the permanent magnets inside the iacv heat up ( slow traffic ) over time they lose strength and the ability to work with the short pulses.
Something changes to deteriorate some iacv's over time and they don't respond well with small steps.
I think the software provides better shaped pulses ( more energy ) as was provided with the old software.
Noticed some half shaped pulses on the owner from spain with his research, starting with a full shaped pulse step is better then a fraction of that value.

We may never know what really happens but this is my best shot at the moment.

VERY logical, Max.
As good an explanation as we may encounter.

If this forum had likes or reputation points, I'd give you a ton.