Today as I was changing the manifold gasket, on my 1990 Ford F150 XLT Lariat, I found that there was a hole with nothing in it. I'm hoping that someone can tell me what goes there. Is it some kind of sensor or should I just plug it ? What goes in the hole on the right ?
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That would be where the air tube would be connected if this motor were in an F250/350, so it's likely that manifold is not original to your truck and you can just plug it.
FYI.. Ford does not put a gasket between the manifold and head originally.

 

That didn't make a ton of noise?

 

I'm thinking that this is where a lot of the noise came from. I thought it was making a bunch of noise because of the gasket leak until I took the manifold off and found that like that. So yeah, it made A LOT of noise.

 

that's to let out the excessive vacuum so the truck will run faster. haha