Duke, I do know how the O2 sensor works. I can see the duty cycle fluctuating on my meter. I've had feedback carbs and fully electronic FI systems. My 260 needed significant throttle to fire (cranks like mad) and I had to keep it revved to keep it running until it warmed up. If I took my foot off the throttle, it would run for 5 seconds until the cold start valve quit and then die. After four or five of those, it would stumble along for a minute or so. It was just way too lean at cold idle, it even sounded "dry". Needless to say, all of this is in open loop. Once warmed up and in closed loop, it ran fine. Until then crapola.

1/4 turn of this magic EHA adjustment screw and the world is wonderful again. Tickle the throttle while cranking, it fires; foot off & it idles like it should. According to Stu Ritter, this sets the lower chamber pressure for the fuel distributor. That's what it regulates the upper chamber pressure on at idle with a cold O2 sensor. Once the O2 sensor kicks in, it just sets the duty cycle to a little more "off time" to compensate. Now I've got to find a CO meter I can borrow to set the "flap" for a nice warm idle. Stu's recommendation is to use a CIS fuel pressure gauge to set the EHA screw. Original spec is 0.40 bar, his recommendation on an older car is 0.45 to "compensate for basic wear & tear and any unmeasured air leaks that have developed over the years." As I didn't have the specialized gauge, I just tweaked the screw a little. It worked, Stu was right.

One of my favorite engneering sayings is "If it happened, it must be possible". This happened.

Richer,

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Norm in NJ
Next oil change at 230,000miles