E304 cylinder misfire after airtube r/r

1999 Tacoma DLX (with SR5 badges, odd) ext. cab 2.4 2wd auto, no mods other than aftermarket cruise control and audio.

I've been trying to figure out what "front" catalytic converter I needed after the muffler shop told me that my truck was CA emission and that there was one built into the manifold. After no luck finding info on it online, I decided to look at it up close.

I unfastened the clips holding the top of the air cleaner, unplugged the MAF sensor, removed the two clips holding the wire harness onto the air tube, loosened the clamp holding the elbow, removed the hose going into the top of the airbox and removed the assembly. As far as I can tell, the ONLY electrical component I messed with was the MAF.

Well, after getting the heatshield off, I discovered there was no cat on the manifold. And considering my dad bought this truck new and never modified it, there never was one. I seriously doubted it was CA emissions anyway considering it was bought from a dealer new in Texas. So I probably have a bad front O2 sensor or bad catalytic, which is the standard one in front of the muffler. After thoroughly inspecting it, I put everything back exactly as it was.

I started the truck and it's running like crap. Hesitating, vibrating, NO power in the bottom end. I drove it a few blocks before giving up and going home. It was dark so I waited until this morning to work on it. Looked it over, could not see any loose wire, hose, etc. Figured maybe I had to reset the computer since I disconnected the MAF. No change, but it did turn off the CEL. So I drove it around, anything above 40mph seems okay but low speeds it's cutting out and I'm smelling fuel. The CEL finally started flashing and then stayed on. I went to Autozone to get a scan and it came back Cylinder 4 Misfire, E304. The truck has stock wires and coil packs and the Denso plugs have less than 15k on them. Had two guys at Autozone look it over, one used to do inspections, and couldn't find a loose wire or hose.

I drove it home, the CEL occasionally flashes. Runs like crap. Picked up a new NGK (they don't carry Denso there) to swap out after it cools off. The plug wires look new, the coil packs have great connection. I just find it very odd that I get THIS problem immediately after messing with the air intake tube. I'm hoping there's something simple I forgot to connect or hooked up wrong. It's just too much of a coincidence for this to have happened and be unrelated.

Help?

 

Update: Changed out #4 spark plug. Looked fine, maybe a hair on the white side. Wet with gas. No oil fouling. Did the resistance test on the coil, but either my tester's going out or the battery's going, because if the resistance was correct that coil should have exploded by now. All the connectors looked great. Put everything back together. I was going to do a spark test, but didn't have a helper handy so drove over to my brother in law's to get his help. Truck ran fine. I thought I'd solved the problem. Went ahead and replaced the front shocks while I was there. Started on my way back home, and it started cutting out again. Not as bad as before, and it smooths out over 30mph and idles okay, not great but better.

Any ideas?

 

Idled and ran fine all day today. Guess it just needed to work itself out, although I know coils can be temperamental sometimes.

 

That code would have been a P0304, just an FYI. As for the cause, check to make sure that you didn't disturb a harness or connector when you did the work that you did. Yes, one would first suspect this, but take into account that things do happen by chance. It could be something more. Ohm each of the wires and compare them. Too high a resistance in one can cause a misfire as well. Might be a good time to go ahead and replace the wires anyway if they are the originals.