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.