fuel injectors on these cars are a breeze.

Bleed pressure by pulling fuel pump relay then starting car. Let run till dies, attempt to start for 3-5 seconds.

Remove engine cover (then throw it out, causes nothing but problems), find the four 10 mm nuts that hold the fuel rail on, undo and store safely on the window cowl. gently pry up on the rail in different areas till it comes out, pull the injector in question out, install new one with new o rings. Reverse and away you go.

Note nut torque spec is 18 inch pounds or so...

So be careful with it.

Cat might result in broken studs which can be a PITA to fix.

Regardless, try removing the pre-cat O2 sensor to see if the problem reoccurs.

If its better, its probably a plugged cat.