I have a 2003 Tacoma V6 (5VZ-FE) with ~130k that just recently started intermittently misfiring while under load (above about 1/2 throttle or so), but only after it's fully warmed up. When I start it cold (and it's plenty cold here in WI) I have no hesitation or any problems until it has warmed up.

It threw a P0304 code (cylinder 4 misfire) when I checked last night.

I'm going to start by changing all the plugs and resetting the code, but if that doesn't work this is what I'm planning on...

1. Check resistance of the plug wires, if it's not in the 10-15 kohm/foot range replace.
2. Check cyl 4 injector resistance, should be around 13-14 ohms IIRC.
3. Swap coil packs and see if the misfire moves, although I suspect that a bad coil would cause misfiring on both cylinders 3 and 4 since they share a coil.

Anything else I'm missing? What confuses me is that it only happens when the truck is totally warmed up and even then it's intermittent.

 

I got lucky and swapping plugs fixed the problem. The old ones were around .060"-.065" gap vs the ~0.043" they should be new. I'm just happy that the problem was the easiest (and cheapest) to fix.

I still don't understand why it would only misfire when under load though, if anybody has some insight into that I'd appreciate the knowledge.

 

Under load, the combustion pressure is higher. This makes it more difficult for the spark to jump the gap between the electrode and ground. The coil makes up for this by producing a greater discharge, but that can only make up for so much.