1992 KA24DE 240 SX, injector replaced, now carbon fouling

[catdrugn]

Wife's car started missing badly. Determined that No 1 cylinder wasn't firing. Getting spark and the plug was good so figured it was the injector and replaced it.

Fired it up, still missing on cyl No 1. Found out I screwed up the o-ring during installation and gas was leaking passed the seal into the cylinder. Replaced the o-ring, re-installed and no leaks. But.........

Now the engine won't idle. It starts but then dies unless the revs are up. And all four plugs are badly carbon fouled. Cleaned the plugs, but the same thing happens again. What am I missing?