How to fill in air control valve passages?
 

The block-off plate I had on my lower inner intake manifold seems to have been blown off, causing an exhaust leak. I had no idea there would be exhaust gases pushing out on it... ah well.

The bolt holes in the manifold are ruined, so I will need to either weld something on, or completely fill it in.

Does anyone know a good way to fill this part up? Would JB weld or something be OK?

I would not use JB weld. It will fall apart over time. Get some aluminum plate stock, cut it to the shape of the opening and weld it on. Since its cast aluminum, you will need to clean the area very well, pre-heat it, and use a tig.

If you are not comfortable with welding AL, you can try tapping a timesert or similar

Used LIMs are relatively cheap. I'd just buy a used one and swap it out. Seems really weird there's be enough pressure on it to blow off though.

I actually tried using helicoils but I didn't drill the hole straight enough and ended up making it worse (cI cut into the passages). Next time, for something in soft aluminum that isn't under a lot of stress, it might be better to tap the existing hole and use a smaller insert.

The reason the BOP came off was because it wasn't even being held on by screws... just by JB stick.

Yeah, used LIMs are a dime a dozen here (I think) but it's such a PITA to actually swap one out compared to taking off the extension manifold and welding on a piece of aluminum.