The BMW Z4 sDrive35i turbo engine suffers from waste gate issues which become progressively worse with normal driving and especially with harsh driving conditions. The turbocharger uses exhaust gas to create air pressure which is then forced into the engine. When there is no demand for power, the exhaust gases are released into the exhaust through a waste gate to prevent the turbo from speeding up. “Waste gate rattle” or “Turbo rattle” is a result of excessive movement between the waste gate and the waste gate seat. This is a progressive issue with the following symptoms:

Rattling at cold start

Rattling upon deceleration

Loss of power

Check Engine Light Illumination

Manufacturer Specific OBD trouble code P30FF

Very poor engine performance and MPG

Adjustment of the waste gate actuator can solve the issue, but the issue will return. If adjustment does not correct the issue, the turbocharger waste gate must be rebuilt with new bushings, or the turbocharger must be replaced. BMW has replaced many turbocharger assemblies under warranty to correct this issue.