2000 3.4L single cylinder misfire P0304

I was hoping to be posting here with a tidy problem, diagnostic, and solution but it wasn't meant to be, so now I'm asking for help.

The patient: 2000 Tacoma 3.4L with 210k miles (plus or minus as it's a salvage title and I have no idea how many miles are actually on the engine)

History:
At around 195k I got a misfire while on the highway and swapped plugs and wires which solved it. (I think plugs were all Bosch DBL Platinum, wires were whatever Oreilley's had I think.)

The Present:
Last week, I noticed it idling rough intermittently, as if it had an occasional misfire. I took it for a quick drive, and it threw a P0304 code and would occasionally lose and surge power. At idle it misfires pretty consistently but it feels like it smooths out at higher RPMs. That may be the misfire going away or the engine just going faster so the shake is less pronounced. Queue the parts cannon:

• I prematurely ordered new coil packs from Rockauto, but quickly decided they weren't a likely culprit so they remain uninstalled. (DENSO 6731201)
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• I pulled and swapped plugs on Cyl 2 and 4 to make sure the misfire didn't follow a plug, but P0304 popped back up.
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• I pulled and swapped coil packs on Cyl 1 and 3 and the P0304 popped back up. (I also left the boot to Cyl 4 resting on top of the intake plenum and got a good strong spark to jump from it.

Must be an injector, right?

I ordered refurb DENSO injectors from Motorwest - $350 (https://motorwestperformance.com/product/upgrade-for-23250-62040/)

and new OEM intake gaskets and a fuel filter from Toyota.
Gasket, Throttle Body 22271-62040
Intake Manifold Gasket x 2 17176-62040
Fuel rail gaskets x 6 90430-12026
Fuel Filter 23300-62010

I swapped my injectors yesterday (3-4 hour job for a dunce. You can do it with Tim's video.) and sprayed a little MAF cleaner at the MAF sensor, but the P0304 popped right back up and it may be running even more consistently rough at idle.

Things I haven't done:

1. Test compression (half because I'm not sure how to do that without borrowing a compression tester and Googling it, and half because the engine sounds even when cranking).
2. Back probe the injector. I don't have a scope (yet) and I'm not the most gifted with troubleshooting vehicle electrics. This seems like the most difficult and most logical next step.
3. Hook it up to a scanner that can actually count misfires. (My cheapo scanner doesn't seem to and the one O'reilley's lent me either didn't or I couldn't figure it out.)
4. Test O2 sensors. I do get an occasional P0420, but I think if it was something like that I would get a random misfire code.
5. Check the timing. I've never even set eyes on the timing system on this truck. My intuition is that if it was timing I'd be feeling more problems.
6. Drain and swap the gas. I put ethanol-free in it from a station outside town half a tank ago. I doubt it's the issue, but maybe? I'm no scientist.
7. Take it to a mechanic. That's my last resort.

If you've made it this far, thank you. What do I need to try next? Put less faith in the P0304 and consider that it may be a different cylinder than reported? Do a compression test and buy a scope? Keep swapping parts? Give up and bring it to a pro? Any and all suggestions welcome.

 

Is it a dead misfire or does it still partially contribute? You can pull the coil off and see if it changes. If it's still partially contributing I'd rule out wiring. Next I'd check compression. It's fairly easy to do and you can rent the tester from Oreillys. If that's good I'd check valve lash. If all of that's good then it gets kinda tricky. You'd want a scan tool and oscilloscope to continue diagnosising.

 

Check your spark gap. May be too wide. Could be easy fix.

 

So you're still running the cheap-o O'Reilly plug wires you put on 15k miles ago after the initial misfire issue right?

I'm wondering if those haven't crapped the bed already as they're notoriously crap.

 

Also, as long as we're throwing parts..

Get those German plugs out of your Japanese vehicle and put the regular copper NGK/Denso plugs in. And a good quality NGK wire set

 

@b_r_o and @Red_03Taco get the gold star. I double checked my plugs and wires. Plugs were good (I misremembered, they're Denso). When I swapped one of my take off wires with the one on cyl 4 it ran like a champ. Found the smoking gun was a tiny hole in the boot (surprisingly hard to see). Ordering some NGK wires now.

Humbling experience. I guess I need to remember to keep it simple.

 

Glad you figured it out