85zx:
That part is often referred to as the "air regulator", because even Z31 FSMs call it that. In fiche-speak it is also a IACV.
E.g.:
The part that phxZ31 is talking about can be called the AAC (turbo) or IAA (NA), and even these names can vary a bit depending on where you look. Sometimes the parts fiche uses names completely different to what the FSM does.
The air reg tends to fail by not raising idle when cold i.e. the bimetal strip that controls the shutter fails. Warm idle is generally not be affected unless the shutter is stuck part way open, in which case the idle speed is raised.
AAC failures can be more complicated. If the motor is adjusted completely to FSM spec, disconnecting the AAC should only result in a drop in warm idle revs of about 50rpm (no headlights on, no aircon etc).
A dubious AAC should only cause variations in the idle speed, not misfiring, since the AAC/IAA and indeed the air reg are supplied with metered air.
All sorts of things can cause idle misfire, like unmetered air leaks or even a leaking EGR valve.
BAADZ:
did the engine miss at idle before the "platinum 4 spark plugs" were fitted?
Edit: Even the factory is not consistent with naming parts in the fiche.
The NA idle-up solenoid and FICD unit is called a "IAA UNIT", the air reg is called an "IACV - AIR REGULATOR", but the gasket between the IAA unit and the plenum is called the "IACV - IAA UNIT GASKET", even though it is on the opposite side of the plenum to the IACV air regualtor.
The IACV air reg does not even use a gasket, it has an O-ring.
Post Edited (Oct 11, 10:12pm)