Scott McLaughlin topped the sole practice session at Iowa for Team Penske despite a late spin.
The Kiwi set 121 laps as Alex Palou and Pato O’Ward set the second and third quickest times.
The IndyCar weekend in Iowa began with a high line practice session to rubber in the higher lane of the circuit.
Chip Ganassi Racing’s Kyffin Simpson and Rahal Letterman Lanigan’s Graham Rahal were given nine-place grid drop penalties for unapproved engine changes ahead of the event.
McLaughlin set the pace early on for Team Penske at 164.979mph before being usurped by Santino Ferrucci.
The field was split into two groups, each given 15 minutes during high line practice.
McLaughlin held the fastest time halfway through before being beaten by Group B’s Josef Newgarden, a six-time winner at Iowa.
Marcus Ericsson went quickest at the end of high line practice ahead of Agustin Canapino and Newgarden.
After a short break, practice 1 got underway at the short oval, and a flurry of cars joined the track.
Linus Lundqvist moved to the top of the timesheets in the opening stages of the 90-minute session ahead of Marcus Armstrong.
Pietro Fittipaldi moved to the top for Rahal Letterman Lanigan Racing, just in front of Argentinian driver Canapino before the Juncos Hollinger driver improved to 181.352mph going quickest.
Ericsson, quickest in high line practice, hit the wall at Turn 3 10 minutes into the session. The rear wing and suspension broke, ending the Swede’s run and costing him valuable track time in the weekend’s only practice.
The sole practice session resumed 10 minutes later with one hour and 10 minutes to go. Palou quickly moved into second place with a 180.967mph.
With an hour to go, Colton Herta had the fastest speed, 182.083mph, ahead of Scott Dixon.
The pace-setter had completed just 11 laps for Andretti, while McLaughlin down in P14 had run 45 laps, the most of anyone with just under an hour remaining.
Further down the order, all three Arrow McLarens of Nolan Siegel, Alex Rossi and O’Ward suffered a quiet session, with the trio outside the top 15.
Ferrucci went fractionally faster than Herta as the track gained grip before O’Ward improved to third place.
McLaughlin briefly held the quickest time before Rossi usurped the Kiwi. Spaniard Palou raised the bar significantly, setting a 185.536mph, a massive three miles per hour faster than his nearest challenger.
Canapino proved very consistent, and Ricardo Juncos, the co-owner of the Juncos Hollinger Racing team, was pleased with the balance of the No. 78 car.
McLaughlin returned to the top ahead of Palou before the session was disrupted once more.
Katherine Legge spun on the exit of Turn 4 after driving on the high line, but the British driver avoided contact with the wall with 24 minutes to go.
With 20 minutes to go, the green flags were waved, restarting the session. Herta held the fastest 10-lap average at Iowa.
Ferrucci narrowly avoided the wall at Turn 4 after getting close to Romain Grosjean and the dirty air coming off the Juncos Hollinger Racing car.
A third Caution was called after Canapino spun. He made minor contact with Dixon in the pit lane but both cars could continue.
Practice resumed with four minutes left, with McLaughlin ahead of Palou and O’Ward. In the closing stages, the pacesetter spun at Turn 4 after attempting to drive on the high line of the circuit.
