Hi there.
I was doing a few things in the engine bay and I came across an unplugged wire after pulling off the air cleaner, which led to this little fella that I have no idea about. It's on a 1971 Cutlass Supreme Convertible 350 TH350 4bbl, and is sitting right in front of the throttle linkage.
I haven't been able to find what it is via the service manuals or any google searching, and any help identifying what it is would be super appreciated!

 

That is an idle stop solenoid. Used on to prevent engine run on or dieseling.

 

Should be in Engine section 6 of CSM, either under carb, tuneup or emissions subsection.

As 4speed has said, idle stop solenoid. Connected, when ignition switch is ON, the plunger will extend out of the solenoid. This is where you set curb idle speed, by screwing the energized plunger in or out to get desired idle speed. When ignition is OFF, plunger retracts allowing throttle plates to close off further and stall the engine so it doesn't diesel.

Some years these things were used to increase idle speed when AC was turned on.

 

Thanks to both of you on that.
I'm not able to find the solenoid in the CSM, only references to a dashpot in this spot. I think this might help me with my idle issue if I am correctly understanding how it works, but I'm still at a loss on where it should connect. I'm not seeing anywhere the wire would be able to reach that it can connect, nor have I been able to find a picture showing it installed with the wiring.

 

It's probably disconnected because 1) it doesn't work or 2) someone didn't know what it does and unhooked it trying to desmog the engine. I have seen things done on a desmog that made you wonder how the car ran.

To test it, with engine off, run a jumper wire from the battery + post to the solenoid's wire. If it clicks, odds are it works. Move the throttle link off idle and see if plunger extends. Then see if it retracts with power off.

I think the power feed wire to the solenoid is green or brown. Don't have my 71 CSM handy, but the power feed wire should be on driver side of engine somewhere, with a plug that mates to the solenoid plug.

 

I'll bet this is a later model carb. My 70 Vista Cruiser had a spring type plunger and my 71 Cutlass didn't have a idle stop solenoid at all. I added one from a later engine. (1973??)

 

The anti-diesel actuator was only used on the 1971 350 in A-body cars. It appears to be a last-minute band-aid and apparently was not originally intended for use when the CSM was printed. I suspect there is a Dealer Technical Bulletin that talks about it.

 

That's a newer carb, probably '73-'74???.Those 2 bosses with the screws that hold the solenoid weren't on '71 carbs. Check the carbs stamping # on the drivers side, It'll begin with a 7 or 17. An original carb for a '71 350 would be "7041250" Yours might be "7043250" or "7044250", The "3" would be '73 the "4" '74, the "250" is a 350 Olds carb. If it ends in "251", it came off a 455. If your car has a/c you could easily hook it up. The main reason they used the solenoids was to kick up the idle with the a/c on. You could tee off the green wire on your a/c compressor clutch & connect it to your solenoid wire(also green). when you turn on the a/c it will also activate the solenoid, kicking up your idle.

 

Learning more and more each day considering I had been operating under the belief it was the original carb. After taking a look, it is indeed a 7043250 carb. This would explain why I don't have an appropriate wire to run the solenoid, as it didn't come with it in the first place (as far as I can tell anyways). It sounds like the "correct" set up would be no solenoid or dashpot at all on a '71 carb, if I'm hearing they didn't have the 2 holes for the mounting bracket. Were there any significant changes between 71 & 73 quadrajets from a performance perspective? I'm going to be doing an engine rebuild in the future and am now considering hunting down a 71 carb ($$$ permitting) to properly match the car, unless the only difference is a 3 scratched on it vs a 1.