P0306 after removing manifold and changing spark plugs

So I had a P0333 and took off the upper/lower manifold to replace the knock sensor harness. Decide its a good tie to put in some new spark plugs (Denso irididum). I put it all back together and I get a P0306. Right off the turn of the key I could tell a cylinder wasnt firing properly - check to ensure wire plug as well seated etc but no go. Any idea what to look for? The harness looks in good condition - wonder if there is another culprit such as me forgetting to hook something back up after the teardown.

 

Did you plug all the injectors back in? 2nd gens will not set codes for injectors so that would be the first thing I would check aside from checking that the spark plug gap didn't get smashed shut during installation.

 

Ok I will look at that in the morning I just pulled the plug out and it has some brown so in the max 5 min runtime I put on it it did fire.

 

You sure your on the right one? #6 is on the driver's side rear.
Nothing got left in the intake ports did it? Seen that happen before too lol.

 

Post #2 mentioned gap. On irridium you should never change the preset gap. It damages the coating.

Havent looked up the code but vacuum or Intake leak?

 

Along with the initial po333 and now the po306 seems like you have several basic test. Both compression and fuel injector leakdown weuld be a start IMO to give a basic direction.
https://axlewise.com/diagnostics/obd-codes/p0306/

 

Yep, it was the injector. Turns out the electrical harness plug was not well seated. Phew!. Thank you for the suggestion.