IAC Valve knowledge

TonyA · May 2, 2025

Charlotte said:
Does anyone remember the size/diameter of the allen screw that adjusters the idle? My iac has been blocked and my set screw is set in a good spot. So I’m hoping to add a nut over the screw and not have to throw it out of adjustment. Hopefully this makes sense?
Thanks!

Charlotte · May 2, 2025

I wondered about the length of the set screw… Thanks for sending those pictures Tony.

comet · May 12, 2025

NonSequiterRex said:
I was surprised to see that it didn't seem to be discussed previously. I was more surprised to see that Norton apparently installed the part without setting the "starting" position for the IAC valve.

The IAC valve has 200 steps between fully open and fully closed. The ECU doesn't need to know the install position as it goes through a learning cycle at either ignition on or ignition off (not sure which). The learning cycle initiates 220 steps, so wherever the plunger is it will be moved to its maximum position (either fully open or closed, not sure which) so the ECU always has a known starting point. You can see this in the IAC settings in SXTune if you have your ECU unlocked.

(Above info courtesy of Matthew at SCS Delta)

I attribute the problems I experienced with high tickover to the valve itself and I'm interested to hear that the same type of problem is being experienced with the Omex ECUs. I always kept the battery charged and my bike would start fine and tickover fine every time. At some point during a ride I would throttle down and the revs would stay around 2200, they might come down after a while. It didn't do this at all for the first 1000 miles or so and when it did start happening it was inconsistent i.e. not on every run. What I didn't try at the time was stopping and restarting the engine immediately after the problem occuring although I've seen reports from others that this resolves it, albeit temporarily. This suggests that the IAC was getting out of sync with the ECU at some point during a run, maybe affected by heat and missing some steps, and the ignition off/on resets it to the known start position, until it happens again.

Just some thoughts.

regental · May 13, 2025

comet said:
The IAC valve has 200 steps between fully open and fully closed. The ECU doesn't need to know the install position as it goes through a learning cycle at either ignition on or ignition off (not sure which). The learning cycle initiates 220 steps, so wherever the plunger is it will be moved to its maximum position (either fully open or closed, not sure which) so the ECU always has a known starting point. You can see this in the IAC settings in SXTune if you have your ECU unlocked.

(Above info courtesy of Matthew at SCS Delta)

View attachment 119741

I attribute the problems I experienced with high tickover to the valve itself and I'm interested to hear that the same type of problem is being experienced with the Omex ECUs. I always kept the battery charged and my bike would start fine and tickover fine every time. At some point during a ride I would throttle down and the revs would stay around 2200, they might come down after a while. It didn't do this at all for the first 1000 miles or so and when it did start happening it was inconsistent i.e. not on every run. What I didn't try at the time was stopping and restarting the engine immediately after the problem occuring although I've seen reports from others that this resolves it, albeit temporarily. This suggests that the IAC was getting out of sync with the ECU at some point during a run, maybe affected by heat and missing some steps, and the ignition off/on resets it to the known start position, until it happens again.

Just some thoughts.

My take on this is that the IAC gets too hot & starts to misbehave - dare one say a design fault. On my 2012 Sport, I experienced idles at 2,500 revs after the bike had warmed up - it would sometimes settle on turn off/on. My 2017 Sport has never had this problem.
You can block the IAC intake pipe so it does not function - this makes starting a little tricky as you have to catch it on the throttle when it fires. Once warm, it started perfectly without touching the throttle.
Another solution was to wrap the IAC in exhaust bandage to keep it cool. This worked & I ran for over 3k miles without problems, thus supporting my heat theory.
A third solution was to make another IAC intake pipe with an on/off garden tap in it. Leave open for starting & then close when warm until the next cold start - nothing like a manual choke.

comet · May 13, 2025

regental said:
My take on this is that the IAC gets too hot & starts to misbehave ..........

That makes sense as it would explain why mine always ticked over fine when cold. They also brought out a thicker gasket to help isolate the throttle body (and the IAC valve) from the cylinder head.

MAK · May 13, 2025

comet said:
That makes sense as it would explain why mine always ticked over fine when cold. They also brought out a thicker gasket to help isolate the throttle body (and the IAC valve) from the cylinder head.

Could it also be a faulty cylinder head temp. sender unit.

comet · May 13, 2025

MAK said:
Could it also be a faulty cylinder head temp. sender unit.

I don't know if that could cause the same symptoms, but it was something I checked at the time as you could see the readings in the SXCar software.

MAK · May 13, 2025

comet said:
I don't know if that could cause the same symptoms, but it was something I checked at the time as you could see the readings in the SXCar software.

My 961 had the engine reving all over the place when the engine got very hot.
Not England!!
A new head temp.sender from Norton cured it.

City Garage · May 13, 2025

The answer is not to use 1980s technology past 2000, like every other manufacturer did!!

Gojuu · May 13, 2025

Kinda makes you wonder if it was supposed to be like this the whole time.........

Torontonian · May 13, 2025

Gojuu said:
Kinda makes you wonder if it was supposed to be like this the whole time.........

View attachment 119759

Guh gugga goo gugga !

TonyA · May 14, 2025

Gojuu said:
Kinda makes you wonder if it was supposed to be like this the whole time.........

View attachment 119759

Hi Gojuu , Where did you find this throttle body ?

speirmoor · May 14, 2025

regental said:
A third solution was to make another IAC intake pipe with an on/off garden tap in it. Leave open for starting & then close when warm until the next cold start - nothing like a manual choke.

I like this idea. Did you install such a valve, any pictures?

Gojuu · May 14, 2025

TonyA said:
Hi Gojuu , Where did you find this throttle body ?

Hi Tony, it’s the AT Power Throttle body.

regental · May 15, 2025

speirmoor said:
I like this idea. Did you install such a valve, any pictures?

Sorry no pics taken - I just used some soft rubber hose & spliced in the plastic tap.

comet · May 15, 2025

This is on eBay if anyone wanted one to play around with:

City Garage · May 15, 2025

There is a brand new one here too!!! https://www.ebay.com/itm/375628753758

comet · May 20, 2025

comet said:
The IAC valve has 200 steps between fully open and fully closed. The ECU doesn't need to know the install position as it goes through a learning cycle at either ignition on or ignition off (not sure which)……

For completeness, the learning cycle is at ignition off and the valve is fully opened. At ignition on it closes partially.

The point about not disconnecting the IAC while the battery is connected has been mentioned before and is worth repeating as it can damage the ECU component that handles the IAC, and that part is no longer available. You’d know if the ECU component was damaged as the IAC wouldn’t move at all.

This all relates to the SC ECU, I don’t know if the Omex one operates in the same way.

IAC Valve knowledge

TonyA

Charlotte

comet

regental

comet

MAK

comet

MAK

City Garage

Gojuu

Torontonian

TonyA

speirmoor

Gojuu

regental

comet

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City Garage

comet

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