Working on a freinds 74 big block automatic. The idle stop solenoid is powered all the time with ignition on. I did a search and I think its being used as an anti deisel stop.If this is correct then to set idle I first disconnect idle stop solenoid power. Adjust idle with screw till it will barely idle. Then reconnect idle stop solenoid and adjust solenoid to desired idle. Do I have this right. Dave

 

I am going to assume it doesnt have AC. Then it is probably an anti-dieseling solinoid, and you method sounds reasonable.

 

You got it right.There is an rpm setting for the low idle but I usually just set it to barely run so it will not diesel.
Oh its an auto- you can always 2 foot it home if the solenoid fails.

 

yes it does have a/c and the other vettes I have worked on the idle stop sol. is energized when the a/c is turned on. This car a little different. Thanks Dave

 

Everything you stated is correct - you got it.

 

Thankyou!!!!!!!!!!!!!!!!

 

Does this 454 with air turned off engage the air conditioner compressor when the ignition is turned off? Some GM cars I believe started with this to put drag on the engine about 1970, I know 70 Corvettes did not have it, but they might have starting in 1971.

 

Not sure what you are asking. There is no power to the idle stop solenoid with the ignition off. Dave

 

As others above have confirmed, you are correct. 73-74 utilized the solenoid as an idle stop to prevent "run on" after engine turned off.

 

...and it doesn't matter if it's an A/C car or not. My very original non-A/C automatic '74 coupe has this.

 

For clarity in case anyone did not know - some Vettes will have an idle solenoid but it may only be energized when the A/C compressor is running depending on the model. My '80 is like that. This solenoid opens the throttle slightly to compensate for the RPM drop due to the compressor load. The solenoid is not used to combat dieseling in that application.

-Mark.

 

Mark
of course it does.
without it, ac needs a faster idle. then it diesels.

 

If your car doesn't have A/C, this would likely be the "anti-diesel" (crappy name, IMO - how 'bout "anti-self-ignition"?) feature. Then you'd adjust the idle with the solenoid DISconnected to the point where it wouldn't even run when hot. Then hook up the (on when the switch is) solenoid & adjust idle, by turning the screw in the end of the solenoid, to proper RPM. The purpose here would be so when the switch is off there's not enough air to run-on at all, preventing "dieseling".

If you had A/C, the solenoid would NOT be powered just because the ignition was on, unless the A/C came on at the same time. Turn off the A/C if you have it & adjust "linkage idle" thus, then turn the A/C ON and adjust "solenoid idle".

As for us, with the Lizard's A/C having been removed with a hammer, and all the bolt-on "Corvette" parts having been swapped for "truck" parts (Bubba wuz hyear ), we're using the non-standard Idle Solenoid in parallel with the non-standard electric fan we added for hot Southeastern cruise days. When the fan goes on, it engages the solenoid to boost the idle speed a few hundred RPM. This gives the alternator the extra spin to power the fan, plus the water pump flows more water, plus the main fan pulls a little harder too.

The idle solenoid is just for an alternate, remotely controlled idle speed, how and when it engages is up to you. Except at Concours, of course.

Just my 2 cents...

 

One of these days, I promise to learn to read.:o

Since you said you DO have A/C, and your solenoid is on with the ignition, I'd have to wonder if Bubba the Wiring Monkey lives near your friend...

Maybe the A/C is always on?

Or maybe it's a transitional model.

Or maybe the BB doesn't notice the wee couple dozen HP the A/C compressor steals... That makes "anti-dieseling" a likely prospect.

From your description (and the follow-ups which I finally processed), I'd have to guess "anti-diesel" and adjust accordingly: Solenoid ON = Correct Idle; No Solenoid = No Air.

Thank you for your patience.

 

This may be a semantic here. The key difference as I see it is in the throttle positioning with the A/C off.

If you have the A/C off in a '80 model and shut off the engine, the carb does not close further. If you have a true idle stop solenoid such as found on earlier C3's, the curb idle is positioned with the key in the run position (with the solenoid energized) and it will close the trottle blades down further when the key is off to prevent dieseling.

-Mark.

 

HEY....... I have a 72 350 auto with a/c and solenoid. when ignition sees 12 volts you can hear the distinctive CLICK the solenoid makes when it turns on when the a/c is on it raises the idle 2 to 3 hundred rpm ........... which is adjustible up or down............. and lowers it when you turn the a/c off . the solenoid is active when it sees 12volts from ignition

Hammadown

 

If you don't have a/c, then you want the throttle to snap completely closed when the solenoid is inactivated - that's what should happen when the key is turned off. When the engine is running, the solenoid is extended and this is where the engine idle should be adjusted.