280z Auxilary Air Regulator (AAR)

Purpose and Functioning:
The AAR is simply a "controlled leak" across the throttle body.
It simulates mildly reving the engine when it is first started (so-called fast idle). 
The fast idle prevents the engine from bogging down and stalling while allowing 
the engine to "warm up".

The AAR is designed to "close the leak" slowly over a few minutes.
It does this by a moving a stutter that closes off the air passage.
The shutter is pushed close by a bi-metal lever.

The bi-metal bends in one direction when it is heated. The heat is supplied
by a heater element at the base of the bi-metal level. Even if the heater 
element fails, the bimetal will be heated by engine heat which is conducted
through the engine and manifold. Later engines had a cooling line run under the AAR.


Properly functioning AAR

Common Cause of AAR Failures: 

• Bi-metal slowly rotates to a position that can no longer operate shutter
  
• AAR gets gunked up by oily engine fumes that are re-circulated. Note that later engines have a revised hose routing to reduce buildup of residue.
  
• Electrical connections to AAR corrode and stop conducting.
  
• AAR suffers mechanical failure due to bi-metal lever rotation.
  

Symptoms of AAR failure

• (failed open) fast idle all the time even with idle set screw all the way in.
  
• (failed close) no fast idle

Trouble Shooting

• If you suffer from a fast idle after the car is warmed up, simply use pliers or vise 
  grips to pinch off the hose between the throttle body and AAR. If the idle rpm 
  decreases then the AAR is not closing.
  

NOTE: Vacuum leaks, a faulty BCCD valve, stuck accelerator linkage, weak throttle body 
return spring or gummed open throttle body flap can also cause a fast idle.

Photos of a common AAR mechanical failure in which the bi-metal lever rotates out of position.

AAR Parts

Cressida AAR variation that can be relocated and mounted to bottom of TB
(note the output port on the bottom... this can feed directly into BCDD ports with proper matching plate)
(note 2. These AAR's have an additional pin that locks the bimetal to prevent it from rotating)

Cressida AAR