Sorry to interrupt your line of questioning, but help me understand what you're trying to do. I'm having a little trouble understanding your idle speed issue.
Idle should be 800 RPM without AC. When aftermarket AC is installed on a Z, it's recommended to raise idle RPM to 1000. That's because it will drop to around 800 RPM (optimum RPM) when the AC compressor kicks in. If one were to NOT raise it to 1000 RPM when installing AC, idle would drop to around 600 RPM for a no bueno driving experience.
I know you have a non-stock cam and other modifications on your car. What was idle set at when you got the car and before AC was installed....1000, 800, somewhere in between?
A Z is supposed to be fun to drive and after reading about the problems you've experienced with your Z for years, I have to ask. Do you have an exit plan for this car?
Dennis