280z Cold Starts, dies when warm.

[Shoetotheface]

49 minutes ago, Zed Head said:

The fuel tweak was for the popping and stuttering, not the idling.

Are you sure that you're disconnecting the sensor?  There is also the cold start (thermotime) switch and the temperature sender in the same vicinity.

Yes. I even replaced it with a new temp sensor. The car runs and leans out with it not connected. Same behavior when it is connected. After wiring up the potentiometer changing the dial seems to do nothing. 

[Zed Head]

Have you checked the resistance at the ECU plug, on Pin 13?  There are many possibilities, including a PO "tuning" around a problem instead of fixing it.  Could be vacuum leaks.  Could be something else.  Another cause for popping back through the intake is a flat cam lobe.  Hope that's not it.

You really need to spend a little time at the ECU connector with the 1980 Guidebook and a meter.  It has all years through 1980.  Make sure everything is right before trying to fix things.  Odds are though that the fuel tweak will still help after you get everything right.  So that's not wasted time/money.

You should check your fuel pressure with the engine not running also.  If it can't get higher than 30 that's a problem.  EFI work is just a long list of small things.