It seems that basically when you are letting the system try and enter closed loop mode its struggling to meet a normal A:F ratio...

I know you have said you have checked for vacuum leaks, but have you physically replaced the idle control hoses? If not, do it...I bet money they are hard as rocks and they are impossible to check the one that tucks down under the intake manifold. They are cheap enough. When I got my 88 300TE @ 64k, they were rock hard and replacing them helped me rid of a vacuum leak I had.

I would start there first

What did you set the potentiometer to? It should be as close to 0.8v as possible. Anything more than +- .1v is too far out of adjustment. So basically you need to be dead on .8v otherwise its gonna idle like crap or stall during different conditions.
Also, have you checked for oil consumption?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k