Idle, Sneeze, Smell... Realted!?

Im new to the forum sorry if anyone finds that fact annoying...

I need help with my Z thats driving me a little nuts.

My Z has this sneeze that wont go away,

Ive replaced my distributor rotor, spark plugs, plug wires, adjusted my spark timing and replaced my air flow meter. Nothing seems to make a difference BUT all parts were messed up in one way or another.

Ive been following specs from a haynes manual (spark gap, timing)

After driving the engine smells like charcoal and burning plastic.

My Idle is usually high (1200-1300rpm) when i adjust the throttle screw to idle around 900 and turn off the car, the next time i start it it will be at approx 400. Also during driving I will get Fluctuations of 800 to 1300.

Im at a point where i just feel like throwing parts at it blindly because they all need to be replaced anyways hahah. Does anyone know if these 3 problems could be related? Any Ideas?

Current plan is to replace the horribly old looking Air Regulator, Throttle position sensor and all vacuum lines.