In 1991 Guerrero was replaced by Danny Sullivan and was left without a car to drive. At the Indianapolis 500 Guerrero drove a second car for Patrick Racing in the No. 40 Sharp's Lola T91/00-Alfa Romeo Indy V8. He qualified 28th and finished 30th after being involved in a crash with Kevin Cogan on Guerrero's 24th lap. Guerrero then drove three select races for King Racing in the No. 26 Quaker State Lola T91/00-Buick V6, scoring a best finish of 14th at the Valvoline Detroit Grand Prix on the Streets of Detroit and the Texaco/Havoline Grand Prix of Denver at the Pepsi Center. Guerrero finally drove the No. 50 Fendi/Hawaiian Tropic Lola T91/00-Cosworth DFS at the Molson Indy Toronto at Exhibition Place, qualifying and finishing in 18th place. Guerrero scored no points for the first time in his CART career and finished 37th in the championship.