My 2003 Pathfinder would not start. Traced problem to faulty throttle body/IACV. Replaced with part from Nissan.(took care not to touch internal mechanism) Performed accel pedal and idle air relearn procedures and car starts and runs fine except that it idles at 1000RPM and throws 0507code(fast idle detected). Every time I do idle air relearn idle returns to specs but when I shut the truck down it "forgets" and the next time I start it the idle settles at 1000RPM once warmed up. If I do the relearn and shut it down and start it immediately it idles in spec, but if I leave it shut down for a few seconds it "forgets" and idles at 1000RPM again. I have tried unplugging the harness at the throttle body and starting from scratch, I have disconnected the battery overnight and I have checked the fuzes. Where does the memory for the idle speed reside once it is "learned"? Did I get a bad part from Nissan. I have seen similar posts to this on forums with no definitive answer. If you have the answer to this riddle I would love to hear it.

Any codes for ISC System?

Just P0507.

Took it to Nissan. Tech said it would remember the correct idle speed if it was reset using their "Consult II". He was right. 20 minutes and $100 later it is reset with no check engine light or abnormal idle for the last two weeks of driving.