Operating temperature issue.
 

My friend and I are stumped. Been doing a lot of forum searching, and Google to no avail.

Here my problem:
I have an 85 n/a 5speed z31.

Ran great for several days and suddenly a problem started.
Once the car hits operating temperature, it begins to buck, backfire, refusing to Rev, and slowly dies and won't restart until it has cooled a little bit.
It drives great when cold, and will not act up until it's at full operating temp
Here is what we've checked:
CHTS is replaced, TPS is replaced, timing has been checked with timing light, unplugged o2 sensor, changed fuel filter.
The fuel regulator is aftermarket with a pressure gauge, when the car is warm and having issues idling and driving, the fuel pressur rreads 20psi. Any ideas are greatly appreciated.

Welcome to ZDriver!

First and easiest step: Check ecu diagnostic codes.

I apologize, I thought I put in that we already did that. It threw 3 codes. CHTS, TPS, andAir CConditioning. We replaced chts and tps.

All codes were cleared, and we even attempted a different ECU.

ignitor likely on the edge of failure heat trips it over. replace or freeze spray it next time and see if that cures the problem.

We tried freezing the ignitor, didn't work.
We got an 87 ecu, and this time it started throwing MAF codes, so we're currently on the hunt for a new one or a cleaning/rebuild guide.

mafs don't go bad that often they are pretty simple devices. Ohm it out per the fsm for a start. codes you get out of the ecu are pretty useless in my opinion. thirty year old technology might have been of some use when everything was new tight and clean but now ehhh. look through the junkyards. any Z31 maf will work . don't believe you can rebuild. cleaning maybe do some good. all it is is a wire thru which current flows and the ecu translates the current as a certain air flow because the air cools the wire and changes the resistance. did you check to be sure the 87 ecu is compatible with the O2 sensor on the 85. if you don't have the fsm xenon31 is a free download. seems to be something to do with engine heat those things are chts and O2 sensor mostly. did you confirm continuity between chts wiring and the ecu. also verify wiring between to ignitor. ground issue? are your battery and battery cables in A1 condition? many a z31 problem can be traced to low voltage not allowing the electricons to function properly (if at all)

I understand the whole ancient technology thing, but it's all we have to go off of right now.
Yes, 87n/a ecu is compatible with 85n/a. I did a lot of research, Xenon and Zbum have amazing websites! :)

The problem is, the problem is ONLY at operating temperature. As soon as the car goes below operating temp(or when the engine is cold), it runs GREAT.

so what else is heat affected? is the egr diaphragm ok. push up on it with a finger it should give then move back to position. 20 psi is rather low on the fuel ring.you say you pulled the o2 sensor connector but have you left it unconnected then driven to operating temp and the problem still occurs. sounds a lot like what happened to a turbo car i knew. cold drive like a dream once it hit op temp awful. turned out o2 sensor bad.

When you changed the CHTS did you also replace the sub harness? you can unplug the connection at the ecu, take a volt meter and check for ohm Resistance. that would confirm that the ENTIRE harness to sensor and all is functioning properly.