ok so out of nowhere my z started running like crap and stalled in the middle of the road. pushed it off the road and it would crank but not start. had a friend tow me home. next day I started up just fine so I test drove it and noticed it was a ok when cold but like 10 minutes after hitting op temp it started sputtering and misfiring and noticably less torque like before. made it home before I was stranded again was looking at it and noticed when you rev bomb it in neutral it spits out a large amount of black smoke (not diesel status but more than a gas engine should) and it felt like it was running on 3 or 4 cylinders. again after I shut it off it would not start, but after being left a while to cool it would. next I drove it very gingerly, 50% throttle max, 3k rpm max, keeping it off of full load as much as possible (according to the tach display) and it still did start running poor after warming up with missing while accelerating but would still drive and didn't stall.
does anyone have any idea what the problem might be or how to diagnose it? the cap, rotor, wires and plugs are less than 6 Months old and it is not over heating, it sits right at normal operating temp.

is it hard cutting at 3k rpm? if so your MAF is dead or has a bad connection. otherwise check the coolant level i have see it when its low throw off the CHTS and it gets a bit weird.

no I have full rev range cold and most of it when hot. it'll sputter and pop for 2 or 3 seconds and then rev right up in neutral. I'll check coolant but I don't expect it to be low. could the chts itself be the issue?

its possible the CHTS normally it will have trouble starting cold. but i suppose it could be how it failed. try checking the codes http://www.xenonzcar.com/z31/ECUcodes.html

it's never liked to cold start as long as I've had it, 40-65 you have to crank for about 10 seconds, 20-40 a bit longer and less then 20 starting fluid is required
but once running it never quit or had an issue no matter the temperature or speed or load until this happened

it very well could be that. but its a bit of a pain to get to. check the codes first. see what you get there. it could be something else causing it too.

I'd start by checking codes. Yes the CHTS itself or the pigtail could be at least part of your problem, you might have multiple issues. The CHTS and O2 and Fuel temp sensor all present in almost the same way just to varying degrees, all worth investigating. The long cranking could be an FPR issue.

so i went ahead and did the ecu codes and it did flash the code for the chts. i looked at the reference table for resistances and at fully warm it should read like 180-200 ohms but it was almost a dead short, so i let it cool overnight and checked it again and it should have been like 8-11 kohm but it was still a dead short so its pretty much the nail in the coffin. then again its over 3 decades old so im actually kind of impressed only a simple thermistor switch is the only thing that ended up dying.

replaced the chts, seems to drive like a champ now after turning up the timing a few degrees. it has its low rpm torque back and i took it up to 70 at wot shifting between 4 and 5k and it never missed or sputtered and the decel exhaust pops are back down to normal (ie it doesnt sound like im 2 stepping anymore). 25 bucks and an hour of work, fine by me!

unrelated question, how likely is the timing belt to fall of the cam gears with the top cover off? its kind of a pain to put it back on without losing a bunch of coolant on the driveway.

As long as the slinger is in place it shouldn't be a problem, many people run with the upper cover off.