Title says it all. Engine starts fine when it's cold, but trouble starting when warm. Will either idle very rough or it won't start at all. It will start most of the time, but I got to give it the gas or it will try to cut out.

I don't know if it's related, but vehicle will also lurch and buckle if it's idling at low rpm/gear as if the throtte is opening and closing instead of staying in one position. If you've ever driven a Z31 you will know what I mean.

Defective Engine Coolant Temperature (ECT) Sensor? You may also need to clean the throttle plate, throttle body, and Idle Air Control Valve.

Well the CHTS and thermostat were both replaced in 2007.

Spell out what CHTS stand for.

Well the CHTS and thermostat were both replaced in 2007.

I don't know what CHTS is an abbreviation for but neither of those two components you've replaced would likely help in this event.
First, the ECT tells the Engine Control Unit (ECU) if the engine is cold or not. If it tells the ECU, "I'm cold," when it's really warmed up, the computer enriches the fuel mixture to compensate. But with a warm engine, that will be too much fuel, causing your symptoms.
Secondly, if your fuel injectors aren't able to spray a fine mist, you won't get even burn times and you'll get rough running and rough idle. If your injectors are dirty and/or sticking, proper fuel delivery is impossible.

CHTS is the Cylinder Head Temperature Sensor. Thought that must be what Texas is talking about because I can't find the ECT anywhere under fuel management or outer engine components in my service manual. Could it be a different name for the 300? Is it the Fuel Temperature Sensor? Where would the ECT be located if I did have one?

CHTS is the Cylinder Head Temperature Sensor. Thought that must be what Texas is talking about because I can't find the ECT anywhere under fuel management or outer engine components in my service manual. Could it be a different name for the 300? Is it the Fuel Temperature Sensor? Where would the ECT be located if I did have one?

What model year is your car?

85

Your Coolant Temp Sensor (CTS) will be located on or near the Thermostat housing/outlet.
Here's a graphic of some of the other sensors on your car:

35804

Awesome resources, CaptainRich!

Thank you, Tx!
If find sharing the artwork very helpful.