930 CIS Question:What's a deceleration valve?
 

OK, I've got all the factory information on the 930 (911 Turbo) CIS fuel system. There's a part referred to as the "Deceleration Valve" (NOT the Aux. Air Valve).

It has a small vacuum hose from the intake manifold by the throttle, and then is has 1" hoses from the pressure side past the charge cooler to the intake manifold past the throttle body. What in the heck is this part for? It was disconnected on my 89 930 Turbo. I've now hooked it up. It doesn't seem to make any difference either way.

Any CIS experts out there?

Thank!

A properly working decel valve keeps the engine rpms from dropping off too quickly when letting off the gas which would prevent a possible engine from stalling as well.


Some have disconnected it and others have adjusted it to drop their rpms faster.

The decel valve prevents the idle from dropping quickly, when you let off the throttle. A useless piece of crap demanded by the smog nazis.
Plug the lines and ignore it.

Thanks Steve and Doug! That makes sense, though I could detect no difference in the car's operation.

Technically, it adds air to the mixture that is left in the cylinders/intake when you lift off the accelerator so there is not a bad backfire. It also helps the RPMs from dropping off too fast so you can shift in the propper RPM range. Good for street cars.

Mike