Ka running on 3 full time problem

So just bought my first 240, bone stock, drove it home ran perfect. Drove around town for a bit, put gasline antifreeze in it went home. Start up next day, it’s missing on cyl 3 only, pull off plug wire 3 no change in it running. Changed plugs, wires, cap and rotor no change. It has spark and compression, will check fuel injector with a noid light tomorrow. Anything Im missing? It did sit for about a year so I’m thinking maybe an injector stuck, but it ran fine when I first got it so maybe the gasline antifreeze gummed it up? Any help would be appretiated thanks

Looks like it’s an injector if anyone has 1 or some they could sell me? 905 251 7115