[Paulporsche]

The deceleration valve is a small yellowish metal unit located to the left of the rubber air flow bellows on the top of the air box (when viewed from the back of the car). It kind of looks like a pear or a small pineapple. Its job is to slow down the decelleration of the engine the way you have described it, originally as a way to reduce emissions. There is a vacuum line connected to its top. You can try disconnecting and plugging that line, as well as the tube on the top of the valve. Or you can try adjusting the valve by turning the nut on the top of the valve that surrounds the tube. I have never done this, but I hear it can be done. When I got my new engine, my mechanic actually left the vacuum hose disconnected and the car ran fine.

If you search, you should find some photos. Or get the 911SC manual from Bentley. Even though it is for SCs, a lot of the info pertains to S models.

Paul