That depends on how you look at it. The Colts in 1998 ended the season 3-13.
In Manning's rookie season he passed for 3,739 yards with 26 touchdowns and set the rookie record for most touchdown passes in a season. But he also set the rookie record for most interceptions in a rookie year. So his first season was definitely one of adjustment, but I don't know that I'd call it garbage. The Colts then went 13–3 the next year, Manning threw for 4,135 yards (so about 400 more), and repeated his 26 TDs but with 15 picks instead of 28.