Cold idle issues

[longtimeacoming]

I have an 89 XT6 that I recently revived after years of neglect. I have fixed most of the issues that I found with it, but there is one last nagging problem that I'm having trouble with and I'm hoping someone can give me some ideas. When the car is totally cold, the idle surges for several minutes after startup, then eventually settles down to about 850 rpm. It will rev to about 1800 then drop to nearly 0 or stall altogether, then back up to 1800 and down again, gradually decreasing it's little mood swings up and down until it settles to normal, usually about the time the temp gauge starts to register. I have already replaced the CTS and pigtail, removed and cleaned the idle control (which seems to operate fine on the bench), and searched repeatedly for loose wires or vacuum leaks. I actually suspect the power supply to the ECM is at fault, because the few times the check engine light has come on, there are no codes logged when I check it, just 333 at the LED on the ECM. On top of that, the memory power for the radio isn't working either, I lose all presets when the key is turned off. It seems to me that the car is re-learning idle etc. every time I start it. I've looked at a few wiring diagrams but that doesn't help much other than giving me the wire colors, I still don't know where any connections or grounds are located. I don't know if it means anything but the green fuseable link by the battery for ECM power was fried when I bought it (which is why I got it very cheap). In other words, HELPPP!!!!

[Rampage]

I am using the FSM for an 88 XT. Hope your 89 is similar.
http://jdmfsm.info/Auto/Japan/Subaru/--Old Models--/

For the radio-
Check fuse #5 - 15amp. It supplies constant 12 volts to the solid white wire on the radio connector. It goes through 3 connectors to get to the radio plug.
It also powers these circuits Auto antenna, Horn, Diode box, Height control unit, Hazard, Trunk room light, Radio, Trip Computer, Clock, Automatic seat belt unit, Key warning switch.

Green Fusible Link- see pics.
Check voltage on both sides of red wire on connector i85(aka i8). Left side of dash.

The wiring diagram shows a connector number, then you go to a chart to get the location number. Weird.

Edited May 12, 2020 by Rampage