What is this?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The item pictured is referred to as an "idle stop solenoid." It is used to maintain curb idle when the engine is running. Once the engine is turned off, the solenoid retracts, which allows the throttle plates to fully seat. This keeps the motor from dieseling. These were installed on smog engines that typically run at higher combustion chamber temperatures. The connector in your picture powers the solenoid, and is sourced from a hot-in-RUN circuit. The solenoid grounds through the carburetor.
If you don't use it to hold your curb idle (meaning you use the conventional curb idle screw on the back of the carburetor to set your idle), you run the risk of run-on (dieseling) after the motor shuts off. If you use the curb idle screw to set the idle and you don't have run-on problems, then the idle stop solenoid is doing nothing. But this is rare.
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