Fast Idle AC Solenoid

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565bbchevy

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Aug 8, 2011
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I am looking for a fast idle solenoid that is strong enough to kick the idle up when the AC is on.
I will have to fabricate a bracket so it doesn't matter if it is universal or model specific.
Looking at Summit's site it seems most of these universal ones are out of stock so something available now is important.
I also see some that look identical but are listed as idle stops but I am not sure what the differences are if they are only momentary.
 
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ELCAM

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Jun 19, 2021
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Idle stop solenoids should work fine, they were to set the correct idle speed all the time (On whenever the key was in run.) the engine was running, when you turned the engine off the solenoid would turn off and retract allowing the throttle plates to completely close.

The were to prevent "run on" or "dieseling" as it was called when the engine kept trying to run after it was turned off which was a common problem in the early smog engine era.
 
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airboatgreg

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Oct 2, 2016
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There were two types of solenoids used back in the day. One would actually push the throttle open and the other would extend when you applied the throttle and hold it open for a higher idle.
 
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383_StealthRam

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Dec 29, 2016
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I doubt any of the "one wire" solenoids are going to be able to overcome the throttle return spring tension unless it's very minimal to extend itself at key on, engine off or after your already running/idling and you turn on the A/C. Most imho would require you give the throttle a little bump to let it extend and then from that point forward your "idle" speed will run at the speed you adjust the solenoid plunger to be at.

If you ever transitioned to EFI (TBI, PFI, etc) this is much more easily accomplished with some tuning parameters but I digress.

In early GM's that also had Idle Speed Control motors (Cadillac mostly) which were stepper motors and allowed the computer to adjust idle up/down for different loads, ie; A/C compressor or low speed turning for power steering assist. Problem is if you wanted to try something like that you would need a way to signal the stepper motor (4 wires) to respond out x counts when A/C is turned on. I'm not electronics expert but there were rudimentary tools made back in the day to test those ISC motors (see below) so you might be able to rig something up with a little research and thought. I had an old Thexton one back in the day. You just want to be careful never to extend them too far out past their normal travel or you could wreck them.

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Another was the Idle Load Compensator (ILC) on many of the Quadrajets in the 80's which basically was adjusted for your curb idle speed, and hooked up to a vacuum source so when the engine experienced a load at idle speed, it would cause the plunger to extend and raise the idle speed a little to compensate. It also functioned as an anti-stall dashpot when coasting/decel so the throttle didn't close quickly when you let off pedal. I looked around on the web and cant believe how much they are asking for those things these days...ouch.

Anyway, something like this might work well since you might be able to use a vacuum switch/solenoid that controls the vacuum to it so it can have the vacuum removed when A/C is turned on which will allow it to extend. How much or how little you would have to play with it's plunger adjustment and internal hex key bleed settings. The factory used a combination ILC-EGR-RVB solenoid block on the left rear side of the valve cover that controlled this along with an anti-diesel vacuum solenoid that iirc just delayed the extension of the plunger when shutting off the car. Here's some info from service manual on the ILC and related items that might help you think through if you wanted to rig up something in this way.

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Lastly, do some research on the 80's GM 4.3/5.7 Deisel engines and how they increased idle when the A/C was turned on...I seem to recall those would immediately jump to a faster idle speed when A/C was enabled but I don't remember if it was through a throttle solenoid/actuator, or an internal injection pump switch/solenoid.

Simplest thing I would say is just go with the one wire solenoid you've already considered and just live with the fact that if you're already idling and turn on the A/C you might need to blip the throttle to let it extend if it can't overcome your return spring pressure on it's own.

Hope this gives you some ideas that help you decide what you end up doing. I'd be interested to know if the ILC option is workable but cost if you had to buy new parts is probably prohibitive vs the simple idle kick solenoids that are a dime/dozen.

Good luck!
 
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565bbchevy

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Since I have a Holley Ultra carb I will have to probably stick with a universal style with 1 wire since there are no mounting points on the carb I will have to make a bracket that mounts to my throttle bracket.
 

84cutspreme

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Jun 4, 2009
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Holley makes idle kicker solenoid. Is this the one thats out of stock?
20-9 bracket
46-74 solenoid
26-57 mounting nut
 
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