How to test Decel valve - 1973.5T/CIS
 

Suddenly my idle after warm up started jumping a bit between 0 and 1,000 and one time almost shutdown the car. It is intermittent. Acceleration and run up through the RPM range was perfect, but only the idle is an issue.

Where to trace?

My first impression is DECEL Valve.

They appear impossible to find new. They are available for the 1974 through 1983 CIS models, but the 1973.5T? Nothing I can find.

Just how do they work? How can they fail? How can you test function?

Anyone..............:confused::confused::confused:

Thanks

Bob

Someone on this board must know how the DECEL Valve works and how to test them. The one for the 1973.5T is no longer available and the newer one from 1974 on, which is still available is not compatible with my CIS set up. That's stinks!

Probably not the DV but to test it remove it and blow thru it. It should be closed. Apply vacuum to small port to open it. You should be able to blow thru it. The DV should hold vacuum


You are most likely running too rich.
First check control pressures

Thanks. Unfortunately I do not have the fuel pressure testing equipment to evaluate my fuel pressures. CIS has always been a pain in the butt and having the first unit in a Porsche 911 does not make it any easier. My model does not have a thermotime switch, air pump and a unique WUR that cannot be adjusted.

According to the CIS Trouble Shooting Guide for a symptom of: Irregular Idle With Warm Engine,
I have to investigate a leaking cold start valve, air leak, sensor plate movement, injector leakage, warm pressure control and maybe the plunger on the fuel distributor getting stuck.

Much to look at and explore.