Sebastien Buemi says his 18th place in Friday practice does not reflect his and Toro Rosso's true potential at Sepang.
After his strong top 10 form in Melbourne, the Swiss driver was near the tail of the field when he took over from test driver Daniel Ricciardo for this afternoon's session in Malaysia, but said he had not been able to put a perfect lap together.
"I only had the one session today and it did not go that well, although we did acquire a lot of data on long and short runs," said Buemi.
"Now, we must look carefully at the figures, because on track, I did not manage to put everything together perfectly: I had a yellow flag, when I was on what would have been my fastest lap on new soft tyres, so in terms of outright lap time it is a long way off what we can do, not reflecting our real pace."
His team-mate Jaime Alguersuari was 10th, but also felt more there was more to come.
"A good number of laps and a reasonable lap time in FP2 after we managed to make big improvements from the morning session," he said.
"In general I am happy with the improvement we saw during the day, but I am still not one hundred per cent satisfied as I believe there is room for improvement from my side and also from the car."