I'd download the factory shop manual from MontyMcV's site for the 89 montero, both volumes, and the procedure is there in the fuel injection section, IIRC. Can't fix these things right without it. The surging idle sounds like a tps problem, and you have to get the idle plate set all right before you set the tps and the idle position switch (in the tps).

The isc is also part of the problem with two coils bad. Good luck in the JY for a used one, most have a failed coil or two. It's possible to take them apart and make a good one with good coils from a bad one soldered in. Replacement is $130ish for the second improved model from dsmisc.com.

Do that idle stop setting and idle speed setting to base idle (have to ground that same mystery wire for this too, I think) and adjust the tps right per the manual, then fix the isc. ISC's are notorious for going bad in these, especially if somebody sprayed tb cleaner into the tb without plugging the idle air hole in the bottom of the tb. Or, just having the coils die because they want to.