Wastegate rattle and tension is only part of the solution to a leaking boost on N54 turbos. If your wastegate vacuum pots are not fully functioning you won't get proper wastegate operation either. You can simply replace the wastegate flappers and clips on your existing turbos but this is a more complete approach.
This kit includes the Vargas wastegate repair kit and new OEM wastegate vacuum pots for each turbo on E9X 335i, 335is, and 335xi (2007-2010). The WG repair kit includes: stainless steel wear bushings, flapper assemblies, wastegate arms, rod ends, and stainless steel c-clips for both turbos. This upgrades the flapper and bushing assembly from 11.5mm to 12.6mm (1/2"). The new assemblies are pressed into the turbo housing and then welded so professional installation is required and the turbos must be removed. Gasket and hardware kits are also available (see links below).
Wastegate rods may be rusty or frozen from exposure so this makes an excellent overhaul with fresh parts that also carry a two year warranty.
