89 sidekick 1.6L 2dr 4x4 A/T

[fixkick]

So I checked the Vin and it does start with a J. Ecu # 33920 60A41. Looking at the website it seems this is the correct ecu. I'm a little confused with the ISC. If its activating when there is extra load doesnt that mean it should be working?

the very first cars Japan, CAMI was not open yet, in canada.'
A4 is AT. A3 is MT

yes this ISC is not working, 
if you have vacuum leaks it can lose control of idle
when you shift from park to drive the ECU sees you do that (a pin on the  ecu goes hot)
then the ECU uses aggressive idle controls do to that huge TC load. on the engine.
so sound like your is sticking,  the ISC up to has 2 dangling wires, make sure those connections are ok
and valve cleaned.
on many of these cars, the valve sticks so the owner hides the bad idle buy opening the throttle stop screw.
but how to do that there are 2 modes, parked or in drive.
if you set the idle with the stop screw, at 800 then shift to drive, the RPM falls like rock.
if you set the hot idle in drive (ouch dangerous) to 800 then back to park idle screams. so you are not this case.
this is also done same way with vacuum leaks the close the TV with the idle screw to hide the leak. 
what is odd is why does idle up work 950rpm IIRC, is fast idle.  head lamps, on, blower on heater or defrost or AC onl .


see page 2 for the diode block for idle up
https://fixkick.com/ECU/89/1990-scan-ECU/allpages.pdf