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Here is a bit of a tute on IAC workings and diagnostics. The guy in the video is not me.
https://www.youtube.com/watch?v=NzEE6OFK2Ao

double post

Nzer wrote:Why does it idle well in Diagnostic mode?
https://vimeo.com/491508087

One reason is that this mode fixes the timing at 10 degrees (or whatever the distributor is set to).
In normal mode, your probably idling between maps, because of the idle fluctuations, brought about by vacuum variations. These maps will also be way higher than would be a standard cam. Once this happens, you are getting a run away effect, where the IAC is trying to correct the idle and it's just a horrible circle of events.
Notice how it gets worse the longer it goes, then it just gives up and stalls.

'quipt4it wrote:

Nzer wrote:Why does it idle well in Diagnostic mode?
https://vimeo.com/491508087

One reason is that this mode fixes the timing at 10 degrees (or whatever the distributor is set to).
In normal mode, your probably idling between maps, because of the idle fluctuations, brought about by vacuum variations. These maps will also be way higher than would be a standard cam. Once this happens, you are getting a run away effect, where the IAC is trying to correct the idle and it's just a horrible circle of events.
Notice how it gets worse the longer it goes, then it just gives up and stalls.

I’m starting to understand. What I’m trying to do is make the IAC air movements less aggressive and minimal while allowing the TB to hold majority of the idle. I don’t actually know if my throttle stop was actually set correct to start with as it’s a XF Ford one that was missing the butterfly.

What I’ve made this morning. Unfortunately I don’t have a 5mm hole punch. Hope one will work.

Exactly
Minimise the input from the IAC, which looks too much anyways, and get the balance from the T/body.
What you are trying to achieve is just the right amount of input from the IAC. Since you have several plates, I would start with the 3mm.
If it's not too much trouble, take a pic of the T/body plate and bore, and maybe one of the IAC

'quipt4it wrote:Exactly
Minimise the input from the IAC, which looks too much anyways, and get the balance from the T/body.
What you are trying to achieve is just the right amount of input from the IAC. Since you have several plates, I would start with the 3mm.
If it's not too much trouble, take a pic of the T/body plate and bore, and maybe one of the IAC

Primary throttle? By plate do you mean the mounting face or the butterfly?

Primary, yes. Try and get one peering into the T/body from both ends.

'quipt4it wrote:Primary, yes. Try and get one peering into the T/body from both ends.

I haven’t got a photo from the backside. Didn’t reeeeealy want to pull it off again.

If you look at the attached photo with the arrow, there is a port.
It starts on the atmospheric side of the blade, does it connect to the underside (vacuum side) of the blade?

'quipt4it wrote:If you look at the attached photo with the arrow, there is a port.
It starts on the atmospheric side of the blade, does it connect to the underside (vacuum side) of the blade?

It’s blocked off for the walkinshaw but for the XF it’s a bleed screw.

Did you get my PM?