Banning the off-throttle blowing of exhaust is a reliability issue for Renault.
That is the claim of Adrian Newey, whose Red Bull RB7 car is said to benefit most from the aggressive off-throttle exhaust blowing in 2011 thanks to its clever Renault engine mapping.
McLaren chief Martin Whitmarsh told the BBC on Saturday that he "has to believe" Renault's reasoning for pushing for the off-throttle ban to be delayed until after Canada.
The FIA wanted to stop the practice immediately in Spain a week ago, but - based on the feedback of some teams - agreed to delay a ban until the next meeting of the technical working group.
Newey said in Monaco that Renault's engines open to full throttle when the driver is not pressing the accelerator "for exhaust valve cooling".
To change that would be quite a big issue
He is implying that an off-throttle blowing ban is therefore a reliability issue for the Renault teams.
"For them (Renault) to change that would be quite a big issue, because the engine's not proven that it would be reliable if the throttle remained closed in that situation," said Red Bull car designer Newey.