Guerrero made his Indy car debut in 1984 for Bignotti-Carter Racing in the No. 9 Master Mechanic March 84C-Cosworth DFX with legendary chief mechanic George Bignotti serving as Guerrero's chief mechanic. The high point of Guerrero's season was a 2nd-place finish at the Indianapolis 500 where he also shared the race's rookie of the year award with Michael Andretti. Guerrero's best finishes outside of Indianapolis were a pair of 5th-place finishes at the Budweiser Cleveland Grand Prix at Burke Lakefront Airport and the Michigan 500 at Michigan International Speedway. Guerrero finished out the season 11th in points with 52 points, only one point out of the top ten. Guerrero won the series' rookie of the year award.