Slartibartfast

How do you like the manual? I've got a spare auto sitting around but part of me wants to swap to manual one of these days... and with 230k on my current trans I may be looking the decision in the face sooner than I'd like. (And don't forget to overfill it!)

If the lights were flickering off, the fuse links would make sense. Flickering on sounds like what they said ^^ about a weird bulb or bad wiring. If something's been chewing on your wiring, the high and low beam wires might just be touching when they wiggle.

There's a tray? First I've heard of one. I guess most original owners broke/pitched/lost them like the sunroof shades. Can you post a picture of this thing?

If the manifold was loose, the gasket could've burned away where it was leaking, explaining the lingering noise. A friend of mine installed an exhaust gasket backwards on his Blazer, and when we pulled it out again, part of it was burned down to the perforated metal core stuff.

You can buy rust converter, basically an acid sort of deal that makes surface rust inert so you can coat over it, and that might help in some places. It really depends on how deep the rust goes. If you find rust, beat on it with a screwdriver. If the metal still sounds solid, grind/treat the surface. If the screwdriver makes a dull thunk and the metal deforms, or it goes straight through, you've got more work to do. I ended up cutting and welding on my '93 to fix some rust-through in the floor, wheel well, and under the battery box. Areas that were only surface rusted I just wire-wheeled to get the worst of it off and then painted it over. The outside of the rig was pretty clean; if you're seeing rust on the outside, definitely give it a good going-over underneath. The real trouble spot on R50s as I understand it is in the front strut towers, so make sure those aren't compromised. Nissan actually had a recall for those rotting out in some states.

There are a lot of connections under the dash, especially the super multiple junction on the driver's side, and if the windshield is leaking, it could be leaking into that mess. You might try turning the A/C on, then spray around with a hose and see where you have to spray to make it crap out again. Maybe try spraying the engine bay around the MAF sensor and the compressor as well. I would also dig around in the driver's footwell looking for moisture, opening plugs, that kind of thing to see if you can find anything after spraying. Odd that it won't code. I don't imagine it's a moisture issue given its location like you said (unless you've been fording rivers). I'm not sure I've heard of an ECU not running codes properly. You can also run codes from the black diagnostic connector under the dash if you don't mind screwing around with some LEDs and a pushbutton--there's a writeup on Infamous Nissan for putting the diagnostic lights on the dashboard that gives you a pinout. Might work if the pot in your ECU just isn't working right or something. Edit: Come to think of it, I don't think you'd have to rig new lights to read codes from the diagnostic plug, the lights on the ECU should flash like usual if you can trigger them from the diagnostic port itself. If you look up the thread on Infamous, find the diagram of the plug that shows the switch hooking into pins 4 and 3. 4 and 11 (IIRC) is also shown but didn't work on mine, I think it's for the four-cylinder or the TBI or something. You could probably screw around with a paperclip and get the LEDs on the ECU to spit codes that way, though you'll need somebody to watch the ECU at the same time unless you have really long arms. Again, this is assuming it's just the little trim pot on the ECU that's not right. I'd want to track down that water-activated electrical gremlin first though.

The transmission was the same from '88 to '95 AFAIK. Should be the same.

Yeah, that's how it flashes through modes. Code check is mode 3. You turn the knob, it starts flashing like you're seeing, then after it flashes three times, you turn it back. Then it'll cough up the trouble codes. Red flashes for tens, green for ones. And the check engine light always flashes with the red LED. I think they're wired together. Nothing unusual there. Not sure what you mean by enabling certain codes.

If you want to add a ground, just pick up a roll of whatever's cheap and black at the parts place. If it's good enough for hooking up aftermarket lights or whatever it'll be more than fine for this. There's probably a screw hole somewhere on the radio you can put a terminal on if you decide you need to.

Reach around the back of the upper intake manifold and you'll find a vacuum line leading down to the fuel pressure regulator.

The '89 manual shows a safety relay, which I'm pretty sure is supposed to protect the electrical system against what your son may or may not have done. Wouldn't hurt to check the fuse links (near the + battery terminal) though. Code 43 shows as throttle sensor in the '89 and '95 manuals. The '89 manual shows just a potentiometer inside the TPS, so testing between the two outer pins should show a constant resistance, and testing between either outer pin and center should show a resistance that varies as the throttle is opened or shut. Now that I think about it, I have heard of some vehicles shutting off the fuel injectors during startup if (it thinks) the pedal is held to the floor. I have no idea if the '87 Z24i was set up with that kind of thing, but it's certainly worth checking. I would also want to check the injectors and their wiring for any obvious rodent damage, and test for open circuits with a multimeter if possible.

I'm not seeing a ground specified in the service manual, so I assume it grounds through the case and the mounting brackets. If you do find yourself staring at a ground wire, put a ring terminal on it and put it under one of the bolts that holds the dash brackets together.

I haven't torn into an idle air system because mine hasn't gone south on me yet, but I don't remember finding anything in the lines that go to it. The idle air system taps into the rubber intake pipe at about the same point as the PCV system (where the gunk comes from), so I imagine most of the throttle body gunk is sucked into the motor before it can make its way into the idle air system. Between that and how you just replaced the valve, unless the idle issue started when you replaced it, I would leave that system alone for the time being. I don't think EGR would cause high idle (assuming you mean 1200 rpm not 12). IIRC it should be closed at idle, and should lower the idle or choke the engine out entirely if you open it manually. My first thought is, how old are your vacuum lines? If you have a vacuum leak, either from the lines or from the rubber part of the intake, the engine will idle higher, and likely rougher as the mixture gets skewed lean. Vacuum hose is cheap. There should be a routing diagram under the hood in case you forget what went where, but if you replace one line at a time it's hard to screw it up. Cleaning out the throttle body while you're in there wouldn't hurt (and actually gave my '95 some power back) but unless there's a glob of something preventing it from closing fully, I doubt the TB is what's making it idle high.

Oil smelling like fuel is a good sign of an injector leak, which matches your code as well. Check your plugs, look for one that's unusually rich or smells of fuel. Hopefully it's 1, 3, or 5 (the ones not covered by the intake manifold). The manifold's not that hard to remove, it just takes more time is all. And try not to run it like that for too long.

Radio on and no sound does sound like an amp issue. Ground for both amps comes from being screwed to the body, there is no dedicated ground wire. Cleaning the points where they ground to the body might help if the wiring checks out. The remote wire supplies + to the amps when the radio's on, but both have a power feed from the accessory circuit as well. My diagram shows the front amp with a red wire for accessory power and a pink wire for remote, and the rear with green/white accessory and pink remote. I think both have to be hooked to + for the amp to work. The radio won't really work without the amps. I tried running the stock radio out of my '95 as a workbench stereo, without amps, and while it did kind of work for a while, it was very quiet and IIRC one of the channels burned out. They're really not built to push speakers without help. The amps, on the other hand... I kept mine after bypassing them and messed with them a bit. It's not difficult to make them work outside the vehicle. The rear amp, a 3.5mm audio jack and cord from the crappy earbuds my iPod came with, a computer power supply, and a couple eight-ohm speakers hot-glued into soup cans were my bench stereo for a couple of years, and that same amp ran the front speakers in my '93 for a while until I could be arsed to install a proper head unit.

Easy enough to test for voltage at the motor connector if the motor doesn't go. If the motor gets power but doesn't go, it's probably seized. You can replace the pump or try to unseize it. The pumps are easy to disassemble, three screws and some tabs to get the motor apart IIRC, and a little steel wool or fine sandpaper should knock the rust off the shaft and the commutator well enough to make it spin freely again. Grease the bushings when putting it back together. This bought me a lot of time with the pumps in my '95 but I did eventually have to replace the front pump due to the lower bushing wearing out to the point that window washer fluid would squeeze out and piddle out the drain hole in the motor onto the wheel well if I filled the res more than half way. But yeah, if the pump works but nothing comes out, check the nozzle. Also keep in mind that there's a long thin pipe going from that pump, through the roof, to that nozzle, so if you haven't used the system in a long time, it may need to prime.

Cap and wires is probably a good start. Knock code could be that the knock sensor is picking up the misfire.

If your phone has a camera, use it. Take pictures before you tear stuff apart to help you put it back together again. Also consider doing some seals on the motor while it's out, they're much harder to get to when it's back in.

I don't know much about the TD series but a knock doesn't sound good. I suspect you'd have issues before warmup as well if the injection pump was a tooth off. Oil in the intake is what I'd start looking into. Could be a bad turbo oil seal. On a gas motor I'd say check the PCV valve, but I'm not seeing one in the TD manual--could just be that I'm not looking in the right place. I would start pulling the intake system apart to see how much of it has oil in it and get some idea of where it's coming from. If the engine is burning its own oil (as blue smoke would suggest) this is certainly something to figure out asap. I have heard of diesels "running away" burning their own crankcase oil.

The dash lights don't go through the Room Lamp fuse (just confirmed on mine). They're wired to the marker light circuit. The fuse for that circuit is on the bottom right of the under-dash fuse box, marked tail lamp (10A). I checked on mine and if you pull that fuse, the dash lights go out. I know you said you checked the lot of them so it's probably not the fuse. Your tail lights and markers still come on, right? If the tail lamp fuse and the markers still work, then my next suspect would be the dimmer. It's not a rheostat like old school rigs have, it's got a big mosfet (transistor) inside, which could conceivably have fried if power got into it on the wrong line. I would unplug the dimmer and test for power at the plug, then try a different dimmer or look up the diagram in the manual and see which pins to jumper to bypass the switch. If the dimmer turns out to be the problem, message me, I think I've still got the dimmer from my '95.

Noticed that my new diagnostic lights were flashing while I drove, despite me not having put them into a testing mode... time to re-read the testing procedures and see what that's about.

Sounds like a bad distributor to me. There's a sensor inside that gets sketchy and craps out as it warms up, then starts working again after it's cooled off.

TC sounds likely to me too. If it was just a solenoid or something I would still expect some response in some gear. The 4x X transmissions are supposed to bolt in with little fuss. I assume the 2x X trans would do the same.

Shouldn't be much of anything different between 94 and 95.

Another vote for the #6 injector.