I have a 03 sedan with a misfire and I’m not sure it’s from ignition coil or vacuum leak, it used to be supercharged but they removed the supercharger before selling it. There is an aluminum cylinder in the top right with 3 blue ended hoses coming from it does anyone know what it is? It was connected to the supercharger and now is just disconnected is that bad?

What it used to look like

What it’s like now

 

Probably just a can for holding more air volume so the brakes don't get hard to operate under boost. Brakes require vacuum, there's a 1 way valve in the brake line near the brake booster. They probably put the 1 way valve before that can, then plumbed the can into the brake booster.

As for the misfire, start by inspecting the spark plugs and the coil packs. Pay attention to any oil in the spark plug well tube, blistering on the epoxy resin ecapsulation on the coil pack (black shiny part on the top), corrosion on the contact spring inside the coil pack well tube boot. If you don't know how many miles are on the plugs just plan on replacing them with stock plugs.

 

Scan the car and see which cylinder is misfiring. Inspect the spark plug to make sure its good.

Then u can swap coils with another cylinder to see if the misfire moves to that cylinder. That’ll tell u if its your coil or something else.