Toyota team president John Howett says the Japanese squad has to "hold its nerve" after a below-par performance at the Spanish Grand Prix.
The Cologne-based team has been among the front-runners since the start of the season, and Jarno Trulli and Timo Glock had started from first and second at the Bahrain Grand Prix.
In Spain, however, both drivers struggled to emulate their performance as Toyota seemed to drop away from rivals Brawn and Red Bull.
Howett admitted the car performance was simply not strong enough at Barcelona, but he believes the up and downs are part of the big rule changes introduced this year.
"There is nothing to say. It is clearly just aero and we had two bad starts, one car was bogged down so we didn't make the predictions correctly and the other looked like it had oil spillage," Howett told AUTOSPORT.
"Jarno had held his position very well through the corners and he was still in sixth or seventh position when Nico came back on the track and he had nowhere to go. Nico was then in front of Timo and with a relatively short fuel load we just sat there behind a slow car.
"Overall car performance was not strong enough with the car updates we brought. You have always a movement, that's why was our car quicker at the beginning of the season than others.
"When you have big regulations change you see swings and roundabouts and we have just to hold our nerve."
Howett also responded to Glock, who feared Toyota could lose ground to the other teams, saying the Japanese team have several improvements coming.
"Based on today's race you could have to say yes, but we have a lot in the pipeline," he said. "It is difficult for me to understand how a driver can make that judgment. I am not sure the drivers know what we are developing always -- I will talk to him about that."
Glock finished in 10th position in Spain, while Trulli retired after being involved in the first-lap accident.