FYI: the "herky-jerky" problem is distinct from the "hiccup", in my experience.
I had the herky-jerky EGR issue when I got my car. Symptoms were: after entering lean burn, the engine would sometimes buck/jerk -- sometimes mild, sometimes annoyingly severely -- when changing throttle position (ie. wanting more power). It went away after cleaning the EGR system (
see my UFO thread)
The hiccup/stumble happens only when entering/exiting lean burn. It seemed to diminish after cleaning my EGR system. "Hiccup" may even be too strong a word for it. Sometimes I can't feel it.
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As for your "self-draining" pack... that's a new one to me too.