The All Blacks overcame a tricky match against France on Saturday with a 26-19 win in Paris.
However, on review of the victory, Foster believes that New Zealand have a lot to work on if they are to avenge their 2012 loss to England at Twickenham.
"We felt a little bit rusty in some of our execution," Foster told reporters.
"The frustrating thing is that we set up the platform quite well, and we didn't really deliver the knockout blow. Some of our final decision-making and a few running lines weren't as polished as they needed to be."
England host New Zealand in their third and final autumn international on Saturday.