So I bought my 04 Z 7 months ago.
The previous owner had installed a few lower end mods including a plenum spacer. I noticed there was orange silicone sloppily around the trim around the spacer. the car ran fine and so I bought it.

Today I got a CEL showing I was running lean. I ran to my mechanics house to help me diagnose it right away. Popped the hood and hurd a leak from WHAT WE THINKKKK is the plenum spacer.
He explained how the air is getting sucked in bypassing the MAF causing it to run lean AND explained thats the reason im getting such sh%^ MPG (18mpg while driving like an honest grandma)

To resolve this ASAP should I purchase two new gaskets (one on top one on bottom) or clean the old silicone off and re-apply correctly?

Im not sure if gaskets were installed previously or not to be honest either

 

I'd go for new gaskets.
Any idea who made the spacer?
Also,noting the silicone,the plenum may have been installed incorrectly.
Not torqued right or,overtightened.

 

its probably the fact the gaskets are kind of frail and easily damaged to due to being so large but having a small width for mating surfaces. try new gaskets first, it could potentially also be warped flange surfaces which would be the explanation for the RTV, personally i hate red though and use grey but i also run a heavily boosted setup.

 

Agreed that it is or seems like it would be comming from this area though correct?

 

What kind of plenum spacer do you have? I use motordyne 5/16," and still use a gasket for a bit of added spacing, but I know you can use that particular spacer without a gasket. I've removed/re-installed my spacer, and even used to reuse that gasket a whole bunch without issue. Maybe if you have a messed up gasket, removing it and running just the spacer (design-dependent) would solve the leak. I don't know about other brands/designs though.

Edit: Wait, ya why do you have silicone above your heads, there's no need for it unless someone half-assed the install at some point.