Evening!

I'm looking at a throttle body and it has a large hole either side of the butterfly - the IAC valve ports.

It also has 2 much smaller holes either side of the butterfly... the one at the top side is around 3mm in diameter and the one on the bottom side is probably less than 1mm. What are these for?

Does it have the usual screw to adjust fine idle, may be it is used for this with an external valve? Just a guess.

Yep - has a screw on the butterfly opening mechanism.

Not fussed about IAC, so just trying to work out which holes I can block off!

I expect they are to grab fumes out the fuel tank via carbon filters.

Is there a screw between the two small holes, like a mixture screw? Some tbs have an air bypass facility for balancing, which sounds like what you're describing.

Any pics??

No screw between the 2 small holes. Not linked as they are on different sides of the TB (top one at 12 o'clock, and bottom one at 3 o'clock).