1990 300zx misfire problem

so heres the problem, spark plugs were changed about 7 months ago(platinum tipped). within the last 2 months my car has had a misfire that has gradually gotten worse which makes me think it is a fuel problem. its now gotten to the point where when i start the car, it will stull out unless i hold the rpm's around a grand for a couple minutes. when the car gets warmer, for some reason the misfire isnt "As bad", but u can definitely still feel it. has anybody else had this problem? i hope its not bad injectors, i think im gonna be taking it sumwhere to get it run on the diagnostics.

what kind of plugs are you using? Are they the right 'temp'? Were they gapped properly?

If that's all ok, check the timing. Check your Throttle Position Sensors. They might be corroded and be in need of cleaning. Make sure you don't have any vacuum leaks, so check your hoses.

If your car is a 90, like I'm assuming, the ECU is an OBDI not an OBDII. Therefore, running a diagnostic is an easy DIY procedure. Because of the age of the car you can't take it to a shop to have them hook it up to a machine. That only works on vehicles that were made in '95 and after. Go here to learn the diagnostic procedure.

http://www.ttzd.com/tech/diagnostictech.html

i actually did that procedure already, bad TP sensor and o2 sensor codes came up, but that shouldnt be causing the car to miss as bad as it is, and the car smokes at around 4000 RPM and higher( which still makes me think its fuel)

well what do you think the TPS does? It tells the ECU how much air is coming in along with the MAF. If it's reading the wrong amount of air, it'll send the wrong amount of fuel. Same with the O2 sensor. The TPS might just need to have the connectors cleaned. The O2's will probably have to be replaced. Either that or check the wiring and make sure that it's not burnt, melted, and/or corroded.

i've had basically the same problem, and yes the 02 sensors will cause it to run bad, replacing them is a pain in the ass, but worth it, if your going to replace all that you might want to clean out your upper plenum, and your throttle boddies with a carb cleaner product, some are specifically designed for fuel injected cars, but if it hasent been done you really need to do it, plus with your bad sensors, its possible you fouled a spark plug, so check them again as well, and like rizzspeed said, make sure they're the right temp, but most of the new spark plugs for the Z come pre-gapped

@ rizzspeed, did you ever have this problem solved? if so, what was the solution? my Z is having the exact same symptoms. Misfire on cylinder 1, dumping fuel and smoke when the it goes past 3500 rpms, its auto put will "stall" if i dont keep rpms up, and after a while the misfire doesnt seem as bad but i can still hear it and there's smoke and fuel coming out the pipes. before i spend on anything or everything @ Gradyman25 said, i wanna know if its electrical; the sensors or wiring, or your Z just needed cleaning