If you own any Audi A4 1.8T or VW Passat 1.8T, or a Golf, Jetta, or Beetle 1.8T built prior to 2002, you should upgrade your factory diverter valve to the latest version offered by Volkswagen. This valve, known as the '710N', has a 14.4 lb spring inside versus an 8.8 lb spring found in the earlier G/J/B models and in all years of the Audi A4 1.8T and VW Passat 1.8T.

The 1.8T diverter valve is responsible for recirculating the pressurized intake air when the throttle plate is closed to prevent turbo compressor stall. The 710N diverter valve will help reduce any surging you may encounter after upgrading your car with a chip, intake, exhaust, or other horsepower parts.

Diverter Valve Location:

Audi A4 / VW Passat: The valve is located on a hose splitting off from the lower intercooler hose between the engine and radiator; access is from underneath the vehicle.
Audi TT / VW Golf, Jetta, Beetle: The valve is located on the rubber intake hose after the MAF (Mass Air Flow) sensor; access is from the top of the engine bay.

This is a factory Volkswagen valve that is also available through your local VW dealer. To determine if your engine is already equipped with the 710N diverter valve, locate the valve and look for this Bosch part number: 0 280 142 114. If your diverter valve has this number stamped on it, you already have the 710N version.