This is for a 1993 Nissan 300ZX 2+2

So ive done hours of research and found many things it can be but ive got the steering wheel shake or vibrations that so many talk about. Doesnt shake at low speeds, does when im braking most the time and sometimes on the highway every time on on it, off and on at any speed randomly. Sometimes I wont get shaking at all whatsoever some rare days or after a long drive itll be gone. Previous owner did take fairly good care of this car and also said the front bushell bearings were bad and what was causing the wheel shake, this possibly it or just contribute or maybe not at all? Gonna lift each side of the car and wobbles the wheel to try and test the bearings...
Other questions are:

TPS going out? Bad harness? Sometimes my Z runs like absolute crap and wont idle worth anything and drives terribly. Rare but every few months it happens and i got an error code from the ecu once but dont remember the code. Usually turning the ecu to flash codes and setting it into standard operation modes fixes this instantly.. Tps sensor tripping itself up and into protection maybe from going out or possible wire/harness going bad?

My EGI relay is missing? No idea why. Wondering what bad can occur from not having it in other than a bypass maybe killing my batt.

Speedo died today. All other gauges work and so does my odometer. Stopped to get gas and it was working and after leaving gas station i noticed it hadnt been doing anything at all.. Smacking the dash causes the needle to jump and go back to resting position, doesnt engage at all but bad solder? Needle come off the gauge? Bad speedo sensor? Usually speed sensors wont feed info to the odo if bad but im just trying to make sure..

Oh and any tutorials on replacing passenger side window roller? Previous owner somehow got the upper roller stuck and got the bolt broke going from the window to the door and was hoping it was about an hour job or so..

Other than this stuff, car runs great and is pretty clean! Good highway mpg too for a sports car!

Thanks for the info and help!

Sorry for the late reply.

Lots of questions here. I'll try to itemize.

Shaking could be a ton of things. Shaking when braking is most likely warped rotors, and shaking at speed cuold be a number of things. I'd check wheel balance first.

The bad running could also be a number of things. With a 93, it could be a bad PTU if it hasn't been swapped to the new style. Other things to check would be harness issues and CAS connection. Also check for corrosion. The ECU code would help me figure it out a lot easier, as it could let me narrow it down.

Speedo could be the cluster itself, a connection, a fuse, or the speed sensor.

As for the window motor, it's a bit like most other cars, but a little more difficult. Nothing a halfway experienced mechanic couldn't handle. I'd budget 2 hours first time tearing into the Z32 door panels, though. And as always, keep the FSM handy.

Oh, and welcome to NICO! Glad you're here!

Hey, not a prob, not a huge deal at the moment, ive got a Nissan 720 pickup i can drive if my 300 gets bad enough.. Not sure about the rotors or if I can check them myself, is there a way i can check or no?
And previous owner said the bushell bearings were going out but i havent been able to check, i just got my car ramps back and found out my roommate had a car jack this whole time. A good one, not a crappy stock one. So i can check the bearings by seeing if i can shake the wheel back and fourth while its in the air. Rear wheels feel like they shake too but putting the car into nuetral dpwn the road doesnt change the shaking so it shouldnt be the driveshaft.

As for the speedo, the sensor should be fine, shows no symptoms of being bad and ive gotten under the car and checked its wiring and under the car it was ok, not sure where the actual wiring harness is in the engine bay though.
Aand the motor is fine, its the roller guide that snapped on the window side and the internal side inside the window is stuck and wont move, the parts like 7$ but its damn cold out here this time of the year and wouldnt want to be out for too long

You can do a visual inspection of the rotors, but not all warping will be visually evident. You may see scoring marks on the rotors themselves. Here's an example:


Here's another, less evident example:


Not sure what a bushell bearing would be...

Now, putting the car in neutral wouldn't have any bearing (no pun intended) on the driveshaft, as power will still be transmitted through the halfshafts through the differential and to the driveshaft.

You've got the right idea about how to check the wheels. Hands at 12 and 6 to check the wheel bearing. 3 and 9 to check steering and tie rods.

Your main failure point for the sensor wiring would be near the sensor itself. And I've seen sensors that have failed look brand new, and old ones work flawlessly. Did you pull the sensor and inspect the gear?

And glad you found the window failure point. Somewhat common point of failure.

Just wanted to update you on the situation, Im still figuring things out but right now im trying to figure my financial situation, Oddly enough, Some days I wont get and wheel shaking at all whatsoever, Not even while braking, others itll be like before, Pretty sure my TPS sensor needs cleaning or is just going out because before driving her for about 5-10minutes, shifting isnt responsive or smooth at all like it usually is and the more gas I give the car, It wont do anything till 3/4 throttle, After driving a few minutes, She runs fine, And some days she'll start up and run perfect.. Also, My alternator belt has been slipping and ive been waiting to replace it, I know it can cause many problems with incorrect readings or something along those lines from the power not being produced at an even rate and very very rarely, the belt has silently slipped enough for the car to shut iself off, Ive had the car for about 6 months now and its only happened twice and started and ran fine no problems right after. My ECU and Transmission ECU both turn up clean as well

If you're having hard shifts, the TPS can be your issue, but it'll usually throw a code. Still not beyond the realm of possibilities.

Rough running could be a number of things. Do a power balance test to isolate, and check your spark plugs. These cars are picky with plugs. NGK PFR6B-11 for N/A, gapped to .044".

But an alternator issue can cause a lot of running issues as well. Not enough juice to power stuff = stuff running poorly. Also could explain the ECU not having any codes stored. There's no long term memory storage on the ECU. Remove power = cleared codes.

And lastly, on the shaking, try giving your driveshaft a good shake. Carrier bearing may very well be going out. Does it seem to shake more when you're off the throttle?

Just stumbled back across this, Sold the Z a while ago but just for others sake if they run across this Im posting an update on my fixes and I am much more mechanically inclined now.

I drove the car a month or so longer with the shaking and it got much worse, The front rotors were warped to all hell. They were some cheap slotted and dimpled rotors and weighed next to nothing so no wonder they warped so easily. I replaced them with some good Powerstop Rotors & Pads made in the USA and the issue was completely gone.

As for the engine running issues, The TPS sensor did go bad, And the wiring for the Knock sensor had faulted. I spliced and replaced the bad wiring on the knock sensor and then replaced the TPS with one from Oreilly's. The replacement TPS actually was much higher quality than OEM and was also a sealed unit, Worked flawlessly after adjustment (Which was a pain). I also figured out that the speedo motor inside the instrument cluster was the issue and never got around to fixing it before selling the car.

I would highly recommend not rewiring a knock sensor, Or relocating it. It may work or you might get lucky and get a little or lot of extra life out of it but do it right the first time if possible and replace it properly, Its an important component.