Hey speedwagon... I'm thinking that one of the issues with your wiring harness could be the giant splice that I did in it... if this is the car I think I'm remembering. I swapped a 1992 loyale engine into a 1987 GL, both SPFI, but one had different shaped plugs for the main engine harness. For some reason I didn't have the original '87 intake manifold to swap onto the '92 (I think I'd sold the engine from the '87 a few months earlier), so I had to splice the round plug onto the big square plug from the '92 intake (or vice versa.... I know that one had a square plug and one had a round). Anyway... I THINK that was this car, that you now have the harness out of... so if there's a big bundle of electrical tape on there kind of behind where the battery would have been on the EA82, unwrap it and you'll find a soldered splice of every wire in the harness. It ran for about 5 years after I did this, but perhaps it went bad on wire 45 in there?? Not sure, and I'm not even completely sure you got that particular frankencar that I'm remembering, but check it out.

I got a new engine harness from the junkyard yesterday and put it in. For the first time, the ECS light went out! Then it promptly came back on, for a code 34 fault.

 

So the IAC issue seems to be fixed, now I just need to figure out why it has intermittent EGR faults.