Foster, who missed two of the first three games this season with a hamstring injury, racked up 155 yards, including a fourth-quarter, 42-yard touchdown run that gave Houston the lead.
The Texans (3-1) prevailed despite losing star receiver Andre Johnson in the second quarter with what appeared to be a hamstring injury. He had made four grabs for 36 yards before leaving the field.
Matt Schaub went 14-for-21 through the air for 138 yards, helping the Texans overcome a blocked field goal that was returned for a touchdown by the Steelers as well as an interception that was run back for a score.
Pittsburgh (2-2) got 16-of-30 passing for 206 yards with an interception from Ben Roethlisberger, who hurt his left foot during the game.
The signal-caller was given an X-ray after the contest, but the results weren't immediately disclosed.