Hello,
These "Constant Idle Solenoids" (CIS) were used in conjunction with the hydraulic pressure switches on the automatic transmissions in the W113 cars with automatic transmissions prior to 1970. Power was supplied to the solenoid any time the ignition was on through fuse #5. The CIS was activated by switching the ground (earth) to the CIS on or off. This was accomplished by the hydraulic pressure switches on the automatic transmissions. One or the other hydraulic pressure switches are activated when the transmission is placed in a forward or reverse gear. These hydraulic pressure switches complete the ground (earth) to the CIS thus activating the device to maintain a constant idle. The hydraulic pressure switches were robust enough to do the switching themselves without any relays. In 1970 the function changed and only USA cars equipped with AC had functioning constant idle solenoids. With these later USA cars, when the AC is switched on, the CIS is activated. USA W113s delivered without AC had a CIS but it was never hooked up! In addition on the later USA cars, a vacuum dashpot was added to the intake manifold venturi to boost idle if the engine faltered on both the cars with and without AC.
I suspect that your W113 may not have been delivered with AC, in addition, most likely you will not have hydraulic pressure switches on your transmission. Do you have the vacuum dashpot on the venturi?
Joe Alexander
Blacklick, Ohio
