GTSBoy

Also, question.....which bearing is stuffed? The fan is bolted to a hub that is on the front of the water pump. It's not a shagged pump we're talking about here?

This. This. A thousand time this.

Almost certainly running lean & therefore very hot EGTs. The hot exhaust makes the dump pipe overheat the firewall & air-con hoses etc around that part of the engine bay and it stinks.

Yes, well, you can't run a Z32 AFM against a standard ECU without Nistune, correct. I would suggest that your IACV would be dirty/sticky/blocked, hence the engine's inability to control revs. But all the roughness could be just about anything. AFM (dying, dirty, broken solder joints), CAS (same), injectors (dirty, broken loom plugs/pins), coils (same). The list goes on.

Well, if it worked before, and you're sure that you have it back together correctly, then the options are; You also messed something else up when you put it back together, which is difficult for us to see from here, or Perhaps having the hoses the wrong way around has caused the variable manifold butterfly to jam (from being driven in the wrong direction perhaps). Can you try to apply vacuum to the hose that should have vacuum and see if what is supposed to be moving is actually moving?

Is that code as translated by some dodgy reader, or from the manual?

As if you only have to buy from the UK. You could get it something direct from Japan, you could probably call Quaife (if you wanted a helical) and get them to make you one right there in the UK. You could go and watch them make it. I wouldn't weld a diff....too crudo 1990s stylo for me. Horrible to live with too. As I said, do it properly, or don't do it at all.

Shimming VLSDs is stupid. Do it properly or don't bother. Just get a 1.5 way Nismo GT Pro kit.

They're the same car at the chassis level.

Not supposed to be different R32/A31 https://justjap.com/genuine-nissan-coil-pack-loom-nissan-hcr32-a31.html

How long is your piece of string? Copies can be anywhere from perfectly fine to absolute death traps. You won't know until you find out. Hit a small rock on the road and have the rim come apart? Possible. Have the thing go out of round because of poor metalllurgy? Possible. Have it be 50% heavier than the wheel they copied because the copy shop doesn't have access to the techniques used by the original? Possible. Or it could be damn near as good. Luck of the draw.

Well, there's also the question of "What category do you want to win?" As it stands, the question makes no sense. You did not specify "just a plaything". Nor budget, nor prep level of rest of car, as per JGTC's point above. As such, my vote is the max option on your list.

It's a stepper motor. If you unmount it from the plenum (and block the holes/pipes it was connected to) and leave it plugged into the ECU, then it will (should) follow the ECU's command to open and close. If you run the engine and set the idle real low, the ECU should try to open it up. There should be little resistance to blowing through it. If you set the idle very high, the ECU should close it right down and it should be quite difficult to blow through it.

Does the IACV work? Is it clean and the valve moving?

AFAICT the only one worth buying is the Tein kit.

Never heard of them. Not a good sign.

It's not the clutch fork that you're going to need to worry about. The little gearbox does not like too much torque being fed to it. You can upgrade to the Nismo pivot, and I think you can get stronger clutch forks, but I would presume that the 350Z fork won't fit, because it's a completely different gearbox. And as I said at the start, the gearbox will die before the standard clutch fork does.

f**kin' Boom! We'd be on at least the 20th generation kittens by now.

That's probably the right diff to physically fit your car. But it is a stock diff, so it's not going to be a mechanical LSD. If it's an LSD at all (and it possibly is) it will be a poxy viscous diff, with an automatic trans gear ratio. That would mean it's probably the same diff as you have now. What you really need to do is to buy a brand new or scondhand 2-way diff centre for your existing diff and get your existing crownwheel put onto it and boost off into the sunset.

Isn't this what measuring tapes are for?

Surely the Laurel has an R200? R230 will not go where an R200 belongs. It's a bigger unit.

He told you he thought it was from a Pathfinder. Did you even google the part number? You know that's a thing, right? My 2s of googling suggests that it might belong to a VQ series, probably VQ25.

The stock idle speed is XXX rpm (let's say it's 650. I can't remember off the top of my head, but it doesn't matter exactly what it is). If the idle speed is lower than the target, the ECU will keep adding timing to try to get the speed up. If the idle speed is above the target, the ECU will wind the timing down to 5° (or possibly even 0°) to try to get it down. And no matter how hard you try, you will never be able to set the screw so that the idle speed is always on the target, so the ECU is always going to be running unusual timing to keep the speed under control. Hot weather, cold weather, air-con, etc, all are able to make the idle speed move by a couple of hundred rpm. That's why we have IACVs.

This is happening because you have removed the IACV. The ECU is trying to raise the idle speed and not getting anywhere (because, dun dun dun, no IACV). So it resorts to advancing the ignition. Put the IACV back on, or change to an ECU that doesn't need it.

Fuel pressure could have changed, injector(s) could be a little dirtier, small vacuum/exhaust leak changing the way it breathes, etc etc. Probably all sorts of sneaky reasons. Even just changing the fuel filter might have done it.