Update:

I checked the lambda and the EHA current. It was very odd. Once it went into closed loop, the EHA current and the duty cycle would slowly climb straight up. The current would go over 20 and the duty cycle would seem to give up and fall to 0% (not 100%, nothing). I could the move the throttle briefly and it would repeat the same process every time. The 02 sensor was sending .7 to .8 volts all the time.

Since I've accumulated various parts over the years, I tried a different CIS computer, 02 sensor, EHA, coolant sensor and intake air sensor. None of these made any difference.

So, as I was about to give up for the day, I looked down at the meters and all was normal! So I adjusted the duty cycle to ~50%. I've driven a couple of hundred miles since and everything is perfect. Not just good, but perfect! No codes, duty cycle is on the money and it runs great.

I mean, it's great that it's fixed. But the problem is it just started working and I have no idea why.

:confused:

Correct me if I am mistaken but it sounds like the O2 sensor output was suspect. I think it should be sending above and below .5 v intermitently if the mix is correct. If this comes around again you might want to try a third O2 sensor to see if that solves it. Glad she's working for the moment. And remember if this should reoccur to pull the O2 sensor wire under the passenger carpet for an easy diagnosis. :D

Yes, I too would like to know the "proper" 02 sensor output.

Anyone?

It fluctuates between 0.1 and 0.9V, it should definitely be a changing voltage. If you get a fixed DC voltage, it is not working OR the computer just cant adjust the air/fuel ratio anymore, you then have to make mechanical adjustments so that you bring the electronic adjustments within the range of operation.