Wahl gained his highest profile and is perhaps best known as the tough but troubled undercover agent Vinnie Terranova in "Wiseguy" (CBS, 1987-90). During his three year tenure on the series, he brought nuanced shadings to his character who often found himself attracted to the individuals he was investigating. During the first season, the interplay between Wahl and villain Ray Sharkey was multi-layered. Wahl established similar rapport with actors as varied as Kevin Spacey and Joan Severance, Stanley Tucci, William Russ and Patti D'Arbanville. Wahl's early TV credits include the short-lived crime series "Double Dare" (CBS, 1985) and the TV-movies "Dirty Dozen: The Next Mission" (NBC, 1985) and "Gladiator" (ABC, 1986). In 1990, he left "Wiseguy" in a dispute with the producers, but his career failed to take off as he had hoped. His subsequently returned to the small screen opposite Lisa Hartman Black in "Search for Grace" (CBS, 1994), a drama that more than owed a debt to Kenneth Branagh's feature "Dead Again". In 1996, Wahl reprised his role of Vinnie Terranova in "Wiseguy" (ABC), but the results were somewhat disappointing.
Health problems were among the factors that have slowed Wahl's career. He was critically injured in motorcycle accidents in 1984 and 1992, and in 1993 was rumored to have a brain tumor (which he subsequently denied). Recurrent spinal surgeries have kept him in headlines but away from the cameras for the most part.