My 87 Brat with EA81-SPFI has been giving me an intermittent code 24. But when I would test it, I would get all the right readings. Finally this morning when testing, I move the harness enough so that it gave me a bad 12V reading. So now I know that the white grounding wire is bad. But it seem to be a shielded wire. Is it critical that it be shielded? Or can I replace the wire with a regular wire? The black/white 12V feed seems to be fine.

The problem is on the harness side? Seems more likely there would be an issue with the connector. The shielding is probably not that important, but not that hard to recreate. Replace as little wire as possible. I have a repair or 2 like this on mine.

Yes. I just traced it to a break in the MIDDLE of the harness on the engine. Odd place for a break to occur, but the wire in the middle is definitely broken.

Fix the break, insulate with heat shrink. Splice the shield also.

I had a wire break on on of mine, just broken inside the insulation. Posibly a random weak spot and maybe some vibration resonated it just right.

Got it fixed. Running much better now... like the ECU actually has control over the IAC! Thanks.