"We found many errors," Marko said ahead of the Chinese grand prix.
"What annoyed us is that they (Renault) were not open. Now there is a constructive cooperation," he revealed.
"We are working hard with both Renault and Toro Rosso. The basic mistake was that Renault started work much too late."
Marko is now hoping the problems were not discovered too late to stop Mercedes from walking away with the title.
"We are optimistic," he said, "because we know we are still not optimal with the engine in some areas. We know to what degree it works and to what degree it does not.
"So it all depends on the development. On the chassis side, we have done our part."
Marko has already claimed that Red Bull's disadvantage to the field-leading Mercedes V6 is as much as 80 horse power.
"We are used to winning with less horse power if you're clever in the other areas," he explained.
"But 80 is too much, especially if you are also significantly worse in the driveability. And Mercedes is also coming to the line with 6kg left in the tank, while we measure what is left in grams," said Marko.