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I have been asked a few times to make a write up on this, so here it is. Since I first purchased my Z32, I noticed a very high engine warm up speed that averaged between 1500 and 1700 RPM. I did not like my engine revving that high when starting on a cold morning with no oil flowing. I also did not like it running that fast before my o2 sensors could warm up and effectively control the a/f ratio. Though the ECU does not totally rely on their input at idle, it does watch them and adjust accordingly. I performed this on my 92 N/A and have run this way for 3 years with no CEL or codes. I do not know if OBDII cars will throw a code by doing this or not. Now there is one less idle component to cause problems. I did some testing and comparative analysis and this is what I found. If I let the engine warm up until the temp needle touches the bottom indicator on the temp gauge, then my fuel economy increases by an average of 1 mpg. If my car warms up at 1100 rpm vs 1500+ rpm, then my economy improves by another 1 mpg. This comparison was done over a 6 month period in a variety of temperatures and conditions. The cold idle speed is controlled by the AICV, and the Air Regulator. I followed the write up on cleaning and testing both of these with little or no change.
[ http://www.twinturbo.net/nissan/300zx/forums/technical/view/920448/Idle-valve-IAA-and-air-regulator-how-to-part-2.html ]
I then noted that the Aid Regulator only operates when its bimetallic strip is cold. That would be during engine warm up. I then proceeded to delete the Air Regulator. It is a very simple procedure. 1. You will need to gather 2 ½ inch vacuum or water caps.
2. Unplug the connector on the Air Regulator ( release/remove the metal clip retainer first)
3. Remove the 10 mm bolts holding the regulator to the plenum
4. Disengage the retaining clamps on the hoses going to the regulator. Be careful as the hoses my be very brittle.
5. Remove the remaining large hoses from the balance and top of the AICV.
6. Install the ½ inch caps on the balance tube port and the IACV port.
7. Install the clamps (from the hose you just removed) on the caps.
8. Start the engine and check for vacuum leaks, and ECU codes.
9. You should now note that on cold mornings your car will warm up at a more respectable 1000-1200 rpm.
10. If you don’t like how this works, it is completely reversible.
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How to Lower the engine warm up idle speed - 
