So the airflow slowly improves as you drive. If so, MB DOC is on target with vacuum leak diagnosis. If the actuator is slowly ever so slowly pulling in, the it's because it's suffering from inadequate vacuum. I,ll bet if you are doing 50 or 60 mph and you get off the gas and coast, the increased manifold vacuum will speed the process up.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.