This has been the hardest damn problem to diagnose.

VG30e, 5 speed transmission. Bone stock engine and trans.

Firstly, it's completely intermittent. Sometimes it's perfect, other times it's terrible. At idle, I can hear tiny stumbling misses. And as I accelerate (manual transmission) it stumbles and hesitates badly. It's worst when I'm in a high gear trying to accelerate from a low RPM (like 4th at 1400rpm) and scales with throttle position. The more throttle, the worse it acts.

Sometimes it happens when cold, sometimes not. Sometimes it's fine cold and gets bad when it gets hot. But when I'm driving it, if it's fine, it will generally stay fine until I turn the engine off and on again, then it comes on hard.

No CEL.

Since it started I've replaced the fuel filter, cleaned the MAF, air filter, oil change, hunted for vac leaks, seafomed it, changed the belts (had a squealing belt, thought it might be the alternator belt slipping) and nothing's made a difference.

I'm going to be doing my timing belt soon, but before I do that, I want to get this sorted. All that's left really is fuel delivery and spark. So the pump, injectors, fuel pressure regulator, plug wires, or plugs (haven't pulled the plugs to check them just yet)

Could a bad distributor be causing this problem? My guess is no, since it's intermittent and not consistent. Same for the plug wires and plugs. I'm guessing it's the pump, injectors, or FPR. Which one should I start with?

An update -

I found the problem. No wonder I couldn't find it, I had to look at night!

#1 spark plug wire is sparking against everything EXCEPT the plug. Through the insulated rubber.

Never seen that happen before!

I also have the same problem, I have changed plugs, cap, button, filter, checked fuel pressure, checked fuel regulator, sprayed engine down with water and i don't see anything arching over under the hood at night...It's causing me to pull all my gray hair out... Any suggestions?

Thanks
Briar