It was scheduled that the governing body's rules clampdown would mean all teams would now have to limit their off-throttle diffuser exhaust blowing to just 10 per cent.
But trackside observers during practice on Friday noted that the Renault runners in particular, notably the dominant Red Bulls, sounded conspicuously loud under braking and in the corners.
Indeed, it emerged that the FIA had succumbed to the French engine supplier's argument that it be allowed to rev its power plants to 50 per cent off the throttle on the basis that it does not ignite the fuel in those circumstances.
In the FIA press conference, McLaren's Martin Whitmarsh bemoaned the situation as "cloudy, ambiguous and changing".
But Red Bull's Christian Horner insisted the FIA has been "right, fair and equitable", with Team Lotus chief Tony Fernandes chiming in by describing the affair as "a bit of a shambles".
Horner however said the original 10 per cent situation gave the Mercedes powered teams like McLaren "a significant advantage", but Whitmarsh hit back by saying the Renault teams now have a "very substantial performance benefit".