CB1100 Idle speed instability problem

[SportsterDoc]

+1 what popgun says. I think the "real" idle fluctuation affects '14's. Mine does what yours does, occasionally.

Ben

Any correlation to low or high VIN?
In other words, any relation to early or late 2014 models?

In cooler weather now, my 2014 starts and idles about 1300, then drops to about 1050, when warm.

If the EOT sends a higher voltage to the ECU than what corresponds to the appropriate temperature based resistance, then the ECU would be expected drive the IACV to a faster idle. This assumes that the EOT has priority input over the IAT. Not much on the internet, other than this forum.

If the EOT values are within spec, and if the wiring is fully intact, then the IACV would be a prime suspect, unless the TPS feedback to the ECU is at fault.

Before getting into all this, I'd first check for a vacuum leak.

Hi Max. Thank you very much for the feedback. After you unplugged your IACV did you try to start it?

I'll give it a try ASAP - been really busy with the holidays fast approaching.

Hi Dave, this is my first reply so it may not format well, anyway...

Here's what i did chronologically:

1 Moved the rear of the tank up and removed the black tb cover with the black plastic screw.
2 bike cold and key off removed the connector from the iacv.
3 key on and " 38 " code was displayed by check engine light.
4 started engine and it fired up around 1000 rpm no problem.
5 throttle response was normal and precise.
6 let engine run for a short while before stopping by turning the key off.
7 replaced iacv connector and switched key back on, code "38 " was not displayed, the startup procedure was restored as per normal.
my cb1100 is from 2010 and imported from japan, does not have the idle issue just for your information.

I am considering making a harness for the iacv connector that has different colour led's in it to indicate stepper motor activity in both direction and mount it on the dash just to find out what makes it tick as i drive around.

Unplugging it would point in a direction ( speculation; either iacv stuck or getting the wrong information from the ecm ) and eliminate carbon fouling or such over time.

i do realise i am on thin ice here and hope some idea's may shed a new light

Cheers max

Input appreciated. 1,000 RPM would be normal idle speed with the idle air control valve deactivated.

Hi Max. Thank you very much for the feedback. After you unplugged your IACV did you try to start it?

I'll give it a try ASAP - been really busy with the holidays fast approaching.

Hi Dave, this is my first reply so it may not format well, anyway...

Here's what i did chronologically:

1 Moved the rear of the tank up and removed the black tb cover with the black plastic screw.
2 bike cold and key off removed the connector from the iacv.
3 key on and " 38 " code was displayed by check engine light.
4 started engine and it fired up around 1000 rpm no problem.
5 throttle response was normal and precise.
6 let engine run for a short while before stopping by turning the key off.
7 replaced iacv connector and switched key back on, code "38 " was not displayed, the startup procedure was restored as per normal.
my cb1100 is from 2010 and imported from japan, does not have the idle issue just for your information.

I am considering making a harness for the iacv connector that has different colour led's in it to indicate stepper motor activity in both direction and mount it on the dash just to find out what makes it tick as i drive around.

Unplugging it would point in a direction ( speculation; either iacv stuck or getting the wrong information from the ecm ) and eliminate carbon fouling or such over time.

i do realise i am on thin ice here and hope some idea's may shed a new light

Cheers max

Be interesting to know how many have cleaned the IACV to solve the issue.
I'm inclined to otherwise suspect that the ECU output is inappropriate for operating temperature...again, if there is no vacuum leak.