I have been trying to track this problem down but so far haven't gotten very far.
I have noticed that on cold start there is no high idle (not sure if there is supposed to be), it starts and idles at about 600 rpm. During this time the economy gauge is a half inch off of economy. If I rev the engine to 1500 rpm or so, the economy gauge goes all the way to the economy side and the engine idles very smooth.
As soon as I notice the temp gauge moving up the car idles good and the economy gauge is all the way to the economy side.
I'm not sure if all of this is related to the black soot in the mornings or not. Can anyone offer any suggestions?