The 1.8T turbo bypass valve is intended to recirculate pressurized intake air when the throttle body is closed to prevent the turbo compressor from stalling. The latest 710N diverter valve, as it is commonly known, helps reduce surging that may occur when modifying your 1.8T's engine. The 710N Audi A4 diverter valve has a 14.4 lb. spring internally rather than an 8.8 lb. spring found in the earlier Golf, Jetta & New Beetle 1.8T motors as well as in all B5 Passat & Audi A4 1.8T applications. This is the latest version made by Bosch and is used on 2002> transverse 1.8T models. If you own a pre-2002 Golf, Jetta, Beetle 1.8T or any model year B5 Passat or Audi A4 1.8T, consider upgrading to this factory installed remedy.