I don't know if it's for emissions reasons, and I doubt it does anything for emissions, but Volkswagen diesels have a throttle that's there to make engine shuto

I don't know if it's for emissions reasons, and I doubt it does anything for emissions, but Volkswagen diesels have a throttle that's there to make engine shutoff much less shaky. It's called the anti-shudder valve, and it activates every time the engine is stopped, and it would stop a runaway diesel.