Interesting. Well, you've basically covered all the alternative items I thought might also be responsible. I had beeni thinking that it might have been a coil, spark, etc. issue, but if you've replaced most of the ignition stuff I guess that's pretty much ruled out.

So it woudl seem it is something related to either the o2 sensor or the AMM. I'm leaning towards the latter given the fact that messing with the harness cured a very similar problem previously, and I'll be checking for oxidation on the underside of those connectors in the near future.

One other thought I had, a bit more ominous, involved a very slow coolant leak in the head gasket. Essentially I was thinking that maybe coolant leaks a little bit into the cylinders after the car sits overnight if its cold (since the head would contract slightly when it is colder). If that's the case maybe its enough to adversly affect the o2 sensor's reading until the trace coolant is burned off and the engine reaches operating temperature.

But wait, isn't the o2 sensor bypassed when the car is first turned on until it reaches a certain operating temperature? Like it doesn't actually serve as an input when teh car is cold but is bypassed by the ECU in terms of mixture?

ARGH... such a PITA. Thanks for the post, I'll look forward to seeing a post on your experience after you r&r the o2 sensor. Interesting that we're having the problem on the same vintage... mine is a 1985 as well.

Merry Christmas.
-rt