Guerrero returned with Team Cotter in 1986 to drive their No. 2 True Value/Emerson Electronics March 86C-Cosworth DFX (numbered 5 at Indianapolis only). Guerrero continued his streak of impressive finishes with a 4th place in the race. Guerrero also scored a pair of 2nd-place finishes, first at the Escort Radar Warnings 200 at Mid-Ohio Sports Car Course and the Miami Indy Challenge 200 at Tamiami Park. In the latter Guerrero qualified on pole position and led every lap, except the final lap due to running out of fuel and handing the win to Al Unser Jr. Guerrero finished the season 9th in points with 87 points.