Roger Clark Motorsport Tumbler Generator Valve TGV Delete Kit w/Thermal Spacers BlackTumbler Generator Valves (or "TGV" as they are most commonly referred to) can be found on Impreza WRX, Forester Turbo and Legacy GT models from 2001 onward. Their prime purpose is to reduce emissions from cold idle to meet standards governed by the EU emissions regulations (similar regulations also exist for both the US and Japan). Whilst this may be good for the environment it does little to aid the performance of your car and it's not uncommon for