Really high idle

[Lord Popgun]

Gordo, the Keihin plug is the Throttle Position Sensor.

[Gordo_imp]

Gordo, the Keihin plug is the Throttle Position Sensor.

Thank you sir! I am not sure what to do moving forward. I may order the newer/updated part#. I am racking my brain not understanding how the new part has either failed, or was faulty or another problem exists, and where that problem is. I go back to a hot, really hot day, mostly being on first or second gear for a long period of time. The procession of bikes was long and took a long time to get to town. The idle got very low and eventually did stall the bike. Once the bike was re started the high idle started.

Titus 2:13
2013 HONDA CB1100

[max]

Something to keep in the back of your mind is that the e.c.u.'s as they have evolved over time have included " strategies " to deal with events like defect sensors, most sensors can be disconnected ( whilst setting fault codes which can be reset ) and the engine will still operate.

Customers appreciate the fact that a map sensor fail is not letting them stranded mid journey and gives the manufacturers a chance of selling the next model in the knowledge that customers won't shy away from their brand just because a connector was not secured, disconnected causing the engine to stop.

Not uncommon for intake sensors to be unplugged and the engine still operates, a diagnostic method to pinpoint a fault.

On the extreme end a temperature sensor in a ford car was indicating 120 deg celcius in a cold engine ( the sensor was broken ) and as a result the e.c.u. in the vehicle concluded that the start mixture was kept lean as per running condition and the car could not be started because the injectors were not providing a rich enough starting mixture necessary for the engine to fire up .

So be careful with conclusions regarding e.c.u.'s, step by step verification usually gets the wanted results and i am glad Dave is helping, he is quite the methodological mind plus has done it before, very hard to beat experience, keep us posted.

So the ecu has different strategies built-in for all possible failures.

Another thing may be the "throttle learning position", after disconnecting the battery some of the "learned values" in the e.c.u. may have to be re-learned, from memory this involves switching on the key and rotating the throttle grip fully-and-back three times and switching the key off again.
The maximum and minimum values for the throttle position sensor will now be "memorized" (because of this sequence) in the e.c.u., just something to try, see if it makes any difference.

Here is a video from one of our members showing how to disconnect the iacv to confirm if it was the cause of the high idle.
https://www.youtube.com/watch?v=uHxmxnRAYw4
Reason for you to try this is to connect the old iacv to verify the connector/wiring/ecu is operating normally ( step 1 ).

From rock climbing i learned to get to the top you make one move at a time, works for most climbers.

[Gordo_imp]

It's interesting that once the iacv was disconnected the idle went back to normal rpms. When I disconnect mine, the rpms go straight to 1750. I will try the reposition trick with the throttle. Anything's possible! Thank you all for taking the time out and supplying me with some ideas and helping me along!

Titus 2:13
2013 HONDA CB1100

[max]

It's interesting that once the iacv was disconnected the idle went back to normal rpms. When I disconnect mine, the rpms go straight to 1750. I will try the reposition trick with the throttle. Anything's possible! Thank you all for taking the time out and supplying me with some ideas and helping me along!

Titus 2:13
2013 HONDA CB1100

Gordo it is possibly helpful to point out here that the procedure i advised was to bring the engine up to temperature and 1100 rpm, at that point the iacv was disconnected and the bike driven with the iacv in that unchanging ( disconnected ) position to isolate the iacv from the rest of the possibilities.
This was known to us and the result matched the anticipated result, however this is not clear from the video if you were not familiar with the sequence of events, so the idle did not drop because the iacv was disconnected, it had been reduced before the iacv was disconnected and remained unchanged during the ride, like a manual butterfly valve screw for idling.
Just to be clear.

[dave]

Gordon, you are more than welcome, it's been my pleasure! Having been there myself (many times) I can feel your pain. I want to carry on the tradition of this wonderful forum to reach out and help a fellow member in need. This forum is full of incredibly talented individuals (much more talented than me), all whom are willing help fellow forum members any way they can. I am confident you'll get to the bottom of this, and I believe I am speaking for all the forum members when I say we're behind you 100%, ready to offer any help that we can. Please keep us updated on your progress.

[dave]

To Max and other talented Forum members: There is a small cylinder threaded onto the IACV electric motor shaft. As the electric motor rotates the shaft this cylinder translates into and out of the port in the throttle body. The service manual states to lightly thread the cylinder completely onto the threaded shaft before installation. If the cylinder is not completely threaded onto the shaft before installing the IACV does this mean the IACV will not function properly, or can the computer sense the position of the movable cylinder and compensate? When I dealt with my high/low idle speed issue the problem never occurred immediately upon cold engine start-up, it only occurred after the engine warmed up, and usually after it reached full operating temperature. If Gordon's high idle is present immediately after starting a cold engine I am wondering if maybe this cylinder wasn't threaded on completely?

[Lord Popgun]

There is no feedback from the IACV to the ECU.

[max]

Good thinking Dave, Popgun is right; on startup the e.c.u. has no idea where the iacv position is so it opens the air valve to the end stop, now it knows the iacv's position.
The e.c.u. then looks at the engine temperature and decides how many steps to close the iacv to arrive at the correct preset value for that temperature and fuel mixture.
From memory the total amount of travel is something like 92 steps and 4 or 6 per revolution.
And during normal operation the iacv also acts on operation of the throttle akin to " assist takeoff " so it is stepping quite often.

If the piston was too far into the barrel it would re-align itself over the next few startup cycles to the position the iacv is happy with, like 2 steps forward 4 steps back, it will always find the back stop.
On a normal warm engine you can experience this iacv adjustment if you start the engine immediately after the key is switched on, the initial idle will be higher and quickly " steps down " to 1050 rpm because the iacv is still initializing.

Another thing that comes to mind is; has Gordo installed the iacv piston so the slide is aligned with the pin inside the cylinder which runs in the piston groove?

[Lord Popgun]

Thanks Max! I knew you would show up and explain the operation—again