The 26-year-old ended his three-month absence from behind the wheel of his Erebus-run Chevrolet Camaro at Winton Motor Raceway on Wednesday, completing a full day's testing.
Kostecki has sat out the opening two rounds (and six races) of the season and said that the test was about “trying to find my feet again".
“It’s just like riding a bike, you have a few wobbles and then you find your feet,” he said.
“I’ve got a little bit of catching up to do but I’m not too bothered. I’ve been working closely with [engineer] George [Commins] and we spent the last three days together.”
The 26-year-old said that he has been behind the wheel of other race-prepared (but non-Supercars) racers at the Norwell Motorplex circuit near the Gold Coast since the news broke on Monday that he would be racing in the third round of the series at Taupo in New Zealand.
“I’ve been out at Norwell a fair bit since the announcement and trying to play catch up,” he said.
“I’ve had a few tune-ups from people around the joint that have been very pivotal in my career so far. But so far I’m pretty happy.”
That comment seems to be a reference to Paul Morris, the former Supercars driver and team owner, who is the co-owner of Norwell. The former Bathurst 1000 winner is believed to have been pivotal in helping to end the rift between Kostecki and the team.
Kostecki will race his Camaro with the number #1 on it, after substitute driver Todd Hazelwood raced with #99 at the opening rounds of the championship at Bathurst and Albert Park.
Team-mate Jack Le Brocq will continue in Erebus's second entry, and currently sits 12th (of 24 drivers) in the championship points.
“It’s great to see a lot of the boys in the team and to be able to run the number 1 and show all the hard work that they put in last year and see all their smiles on their faces has been cool,” said Kostecki, who like all the series' drivers, be racing at the Taupo track for the first time in a Supercar on 20-21 April.
“Anything is possible. We’ll focus on ourselves, how we did last year, and we’ll see how we end up.
“But I’m pretty confident we’ll be up towards the front.”