I heard when computers go bad in these it's generally the capacitors on the PCB. Which can slowly get worse until finally they just can't give the computer the voltage that it needs. Causing it to do all sorts of weird stuff. (that's how I understand it anyways) happened to an old desktop I own, I replaced the caps on the motherboard, and it's good as new.
I know the EEC-IV isn't very powerful at all, but I imagine it's similar in more ways than not.
I'm leaning towards it being the computer. You're right, a lot of wiring doesn't just instantly go wack, otherwise it would probably be quite obvious.
Maybe where the main harness connects at the firewall?
As a quick re-cap, if the IAC is plugged in, it will stall right away after starting up.
Whatever I did the other day... just plugging/replugging in sensors and vacuum lines and moving stuff and wiggling stuff... I was able to plug in the IAC once again and run the car. It was running how it should be in my opinion.
I thought I had solved the problem by accident, so I wrapped everything up and posted on here in rejoice.
When I went back later to use the truck again, the problem was back.. it stalled instantly because the IAC was plugged in.
The fact that I got it working by fiddling with stuff, I feel, rules out so many possibilities. Can't be anything "broken", because if it was broken it wouldn't have started working again. Can't be anything electrical being faulty, because if it was faulty it wouldn't have started working again?
That leaves us with things like... kinda like having a phone charger where the wire has to be bent a certain way in order to charge your phone.. I never knew why phone chargers did that.. Do you know Murkin?
Because if we knew that, that's more than likely my problem.. considering it worked one day, didn't work the next, then worked for like 15 minutes until I left it alone.