The hose I've highlighted in green - what does it do? Gets pretty deep under the intake so I can't trace it back without pulling the intake again.

What would happen if this hose was not connected here while the engine ran at idle in park, neutral, reverse, and drive?

I missed it when getting things back together after installing new injectors. Coolant leaking from mid to top of motor somewhere after reassembly but I can't find any traces of water at or below the intake gasket. Hoping this little hose was the culprit.

Thanks.

 

yup...coolant hose.

 

Yep, ran it some more after reattaching it and all good on the water front. Burning off oil on both headers now. Don't see any active oil leaks but smells like oil burning and smokes. Freaking valve cover screws were just less than hand tight all around so I got them just over hand tight and trying to burn off the excess. Taking a while though.

Parked the car all of last year until three days ago. Didn't expect a valve cover gasket leak from sitting.

 

To answer one of your questions that I didn't see addressed here already - that coolant flow is there at the intake manifold, I'm pretty sure, in order to prevent the throttle body from icing up in cold weather conditions.