I think you're absolutely right Roger.
My old Silvertop Zetec had an aluminium throttle body which also had a small 2.5mm hole in the butterfly to assist the idle airflow but when I came to fit the new Blacktop engine it had a plastic throttle body with the same black lumpy sealant on the butterfly.
Being keen to promote the cleanest possible airflow, I of course cleaned up the butterfly whilst scratching my head as to why they would put this horribly gunky stuff on to an already thick butterfly.
Only then did I see a small sticker warning the installer NOT to remove the sealant otherwise running problems might occur.
As I have said several times on this forum "We Live and Learn" (I think I'll have that put on my gravestone).
However as luck would have it, That sealant is only really needed with the OEM ECU which as calibrated to open the Idle air valve assuming no air is getting past the butterfly. If some air was getting past the butterfly, it would cock up the OEM calibration.
As I'm using the Omex ECU, we do it slightly differently and indeed I have drilled a 2.5mm hole in the butterfly to work in conjunction with the Idle air valve.
On normal temperature tick-over, the IAV is hardly open and is used more for cold start tick-over or as a sort of anti-stall valve.
This is similar to what you would do with ITB's where there is an idle adjust screw on the butterflies to crack them open slightly for tick-over.
Ah, the joys of clever modern engines.
