Kimi Raikkonen says he did not show the true pace of his Lotus E20 during Friday's practices for the Malaysian GP.
Despite a solid pre-season, Raikkonen has been hit with several issues as he makes his return to Formula One.
Steering problems hampered his efforts at the season-opening Australian GP and with that issue was somewhat resolved on Friday, the Finn was hit with KERS concerns.
As a result, Raikkonen finished the day down in 15th place, 1.524s behind Lewis Hamilton's P1 time.
"It was an okay day but we still have work to do on the set-up," said the 2007 Champ. "The steering was a small improvement but we are still working in this area.
"I feel fine in the car in the hot conditions, and the race will take place later in the day so I don't expect that to be a problem.
"I hope we will make some progress tomorrow as the car is quicker than we've shown. Having an issue with the KERS in the afternoon was frustrating but I'm sure we'll have it fixed for tomorrow.
"The track is exactly as I remember it and I hope for a better qualifying than we had in Australia. I'm looking forward to racing here."
Raikkonen's team-mate Romain Grosjean had a better day, and a better time, as he brought his car home in eighth place, 1.139s off the pace.
"Today went pretty well with a couple of small interruptions to my sessions," he said.
"In the morning there was something not quite right with the rear of the car which was soon sorted, then in the afternoon I picked up a cut on one of my tyres. Neither was a major issue.
"We looked at dealing with the heat and finding a good set-up for the high track temperatures here. This track feels fantastic in a Formula 1 car.
"We're not quite there with the set-up, but we have plenty of data to work through. I think we've got a good idea of where to go for qualifying tomorrow."