It was at premier customer Red Bull’s behest this year that Illien was drafted onto the project, following early problems.
“The first few races, power was one thing (problem),” driver Daniel Ricciardo told the BBC, “but (with the) driveability I was getting a headache from my head getting whiplash.
“There were a lot of splutters going on when I got on the power. That made it nearly impossible to win this year,” the Australian added.
Renault cannot hide that early 2016 did not go well.
“We arrived at the first winter test believing that we had made a big step forward between seasons,” operations director Remi Taffin said this week. “We genuinely thought that we had done a good job.”
But he said that the struggles of 2014 had been so difficult that Renault erred in fixing a “cocktail of problems” for this season.
“We wanted to make up the gap so badly that we pulled the rug out from under our own feet,” said Taffin.
For 2016, however, there is optimism.
Renault will continue to supply Red Bull, but the team will be merely an unsponsored customer with re-branded ‘Tag-Heuer’ power after the relationship broke down in 2015.
The French carmaker, meanwhile, has bought back its former works team that is currently known as Lotus, and Renault will also continue to work with Illien this year.
“We did not see the full extent of the collaboration (with Ilmor) in 2015 for various reasons, but now they are under our control and we have a clearer direction we should see this more in 2016 and beyond,” said Taffin.
He said the 2016 unit will be on the dynamometer in December so that Renault and Red Bull can “go to winter testing without any issues”.
“Naturally there are some details to sort, as can be expected, but this is really only refining and we are in much better shape now than we were at this point last year, for sure,” Taffin revealed.