I had always assumed that idle speed had a few distinct "levels", such as "initial start", "warmup", and "normal operation".  After watching my coolant temps and idle speeds real close the last few weeks, I've found that not to be true.  Appears to be a continuous range.  Explains why I don't get ISC failure MILs, despite the idle being out of "book spec"...  Seems the ECU has a different idea of what's normal than what they put in the book!  Probably one of the hazards of having an "OBD 1.9" car (Known to have some bugs that won't let it pass an OBD-II test (which is fine, as it's a '95 and OBD-II was not required yet), but has all the OBD-II sensors/goodies).

During a cold start (like below freezing), the Eclipse idles at 2500rpms on initial start and smoothly comes down to 2000rpms as the O2 sensor starts to heat up.  It then continues on down to 1500rpms as coolant temps reach 40C.  By the time the coolant reaches 80C, we're idling in the 1000-1100 rpm range.  This temp/idle combo is frequently seen even once fully warmed up after getting off the expressway on a below freezing day.  At around 82-83C, the car is idling at 800-900rpms now (just outside of the factory 750+/-50 rpms specification).  This is the normal coolant temp for my car in operation (hood closed, sufficient airflow, not a super hot or cold day, etc.).  In order to see the normal factory idle, my car needs to be at around 85C, which is quite rare, only happening on super hot days if I manually force the fans on.  Once the coolant temperature reaches 90C, the idle is now in the 600-700rpms range and the oil pressure light will just flicker a bit here and there if we're all the way at the bottom of that range.  The car WILL get coolant temps this high pretty easy on a warm day in traffic as the fans don't automatically kick on until 95-100C range!

Note that the BISS was set per the factory instructions, with one slight exception in order to get the car within specification.  After removing the diagnostic equipment, the idle dropped from 750 to 650 immediately.  In order to get within the spec listed in the factory manual (750+/-50rpms), I had to take 1/4 turn out of the BISS.  That got me 700rpms exactly.  Procedure was carried out with the hood open and the fans off.  Coolant temp stabilized at around 86-87 in that configuration.  Interesting that locking the ISC and timing results in a 50 rpm bump UP in rpms though!  When the car had a VPC, that never happened, but just started now that it's been returned to stock...  Wonder if the "true" OBD-II DSMs ('96+) are a little better about getting that 750+/-50rpm spec in wider coolant temp ranges?  I don't have a coolant temp gauge on my OBD-I MR2, but it seems to have a very wide idle range as well, going anywhere from 500-1200rpms based on conditions, but normally falling somewhere between 750-900 (lower numbers seem to be associate with hot days, higher numbers with cold days).