| I have been diving into the idle control / PID section of the Haltech Elite 2500 lately and will eventually put up a full article explaining step by step how to dial your idle in. During this process I have found some interesting things about the Z’s idle system and thought some of you might like to see as well. This is a great resource for getting the basics done on what’s happening behind the scenes to make your car idle well.
https://z32.wikispaces.com/Idle+Control Cliff notes:
AAC: primary control unit.
Fast Idle Control: raises the rpm’s when AC kicks on or heavy load from power steering occurs.
Air Regulator: spring that heats up and slowly closes allowing more air when the engine is cold for proper idle. This system always seemed stupid to me and like typical 90’s Nissan over engineering. There are 3 separate devices that need to work in unison to provide a good quality idle. Why not just have one? During the process of changing over to the Elite I decided to unplug the FICD and the AR and test the limits of the AAC. I wanted to see how quickly it could react to change and what RPM range it could control. The results where interesting. As the video starts the car has already been brought up to temp (178) and is targeting 1K rpms to idle. It is taking the AAC stepper motor a duty cycle of ~ 29% to achieve this. 
The first change that I make on the keyboard is to switch the target idle from 1,000 RPM’s to 0 RPMs. The AAC then goes to 0% (fully closed) and the RPM’s can only fall to 930-950 ish. This floor is based on the position of my throttle bodies and the position of the set screw on the IACV. 
Next in the video I set the target idle to 5000 RPM’s the system didn’t like that number and only allowed for a max of 3K. I entered 2K. The AAC quickly shoots to 100% duty cycle and the RPM’s normalize out to 1800-1850 ish and at that point it can’t open any wider to let additional air in. 
By testing this I know now that the AAC is capable of controlling a ~900rpm range without the assistance of any other devices. Why would you ever need more range than that? I think that by bringing my set screw or throttle bodies down some this range could be even further extended but I don’t really see a need for it.
Here is the video showing all of this happening real time.
YouTube Link Clicky Clicky Thought some of you might find this interesting as well.
Madhatter10-6
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Idle Control Fun with Haltech Elite 2500 Video - 
