engine rpm surge. help needed.

[fixkick]

yes, i missed the "BY 100" sorry.


so it has vacuum leaks, and more. where unknown.
the 100 rpm drop means (if ISC does close) that the there are huge vacuum leaks.
the IAC is one of the very first tests.
why? because it works using same technology as a coolant thermostat (wax) not one lasts this long? 20 + years.
a vacuum leak make all other work very very hard to complete , cases in point.
setting spark timing
testing the FPR with RPM wrong (or out of scale with throttle)

there are only 3 normal air paths.;at idle.
1: bleed screw (duty cycle calibration is not for RPM at all and when does, that means its dead, as in cant regulate idle)
2: IAC (closed hot , over 150f closed if the wax magic fails, this fails hard or 150f is way off calibration now)
3: ISC (modulated by ECU 200 times a second hot to control RPM at all times.
4: leaks, illegal leaks.

when you see the bleed screw(and screwdriver) change RPM that means the (ISC/ECU) is out of control HOT.
if you close the bleed gently, CW, and rpm is not at 800 (grabbed by ecu) on the way closed , the same. facts. (leaks)
nature loves to add fresh air to vacuum, that is it's job, (on earth) it wants to find a way and does so with unending talent.(insidious)