Idle stop solenoid wiring

[tk1251k]

NY 72 gmc 350 automatic tranny has the stop solenoid on the Quadrajet carb. I have not power to the idle solenoid maybe that is why the truck hardly idles in drive with brakes app;ied. Followed the wiring to underatt the truck where it is hanging with another wire both unplugged.Question is I cannot find a place where they would pug to but seems they would plug to the tranny somewhere Anyone have a similiar truck they could check or infor. thanks

[67 chevelle]

is it an ac truck ? , sounds like the idle step up solenoid , it would only have power when ac is on

The kickdown solenoid would be in the back of the carb for wot , or I have seen them under the gas pedal , not sure your year trany would have an electric kickdown , most were cable or rod operated

[tk1251k]

It does have a/c. Having trouble at idle with foot on brakes. I know the idle solenoid has not been connected for some time at the carb. i traced wiring to underneath pass, side of tranny where it branches off to two unconnected plugs. So it looks like from the way it hangs under the truck and clamped it both wires should coonect to trans. or starter somewhere.

[brown7373]

I have the opposite problem My solenoid has power all the time regardless of whether the A/C is on or off. The wiring to the transmission is for the transmission controlled spark. Not sure if it has anything to do with the idle stop solenoid.

[tk1251k]

I just cannot locate where the two wires might plug into to check things out. Power has to come from somewhere just need to find out where.

[tk1251k]

Originally Posted by brown7373

I have the opposite problem My solenoid has power all the time regardless of whether the A/C is on or off. The wiring to the transmission is for the transmission controlled spark. Not sure if it has anything to do with the idle stop solenoid.

Where does the wire leading from your idle solenoid plug into? Mine runs across the back of the engine to pass. side down by the tans. where its hanging loose with two plugs not plugged in.

[brown7373]

My wires hang loose too. I think the TCS switch (s) has been removed from the transmission long ago. It has 2 terminals with the spades at 90 degree angles. Many people disconnected and disabled the TCS right after they bought the truck. In addition to my truck I also have a 72 Cutlass and a 70 Bonneville and neither have any of the TCS. I bought the Bonneville in 1979 and it still had the switch on the intake, but the system itself was bypassed and missing from the transmission. The TCS only allows vacuum advance in high gear, or if the engine is overheating. I'm not sure it would have anything to do with the A/C. My wire comes out of the taped wiring harness and I am not sure what triggers it, and reading a wiring diagram has never been my strong suit.

[IHeartGroceries]

Interested in the final resolution.

Having the exact same idle issue. Haven't looked too deeply into it. This thread certainly helps.

[tk1251k]

Thanks for the info. So I guess your idle stop solenoid is unplugged or not working either. This one has been unplugged for many years I know just occured to me it might be part of the problem with idling at stop. But since it seems it is only works when a/c is on may not be of any help with a/c off.

[tk1251k]

Just did some wire chasing discovered the the pink wire from the idle solenoid goes across the back of the engine into a harness and runs to the fuse box where it was unplugged. I have had the truck for 33 years never unplugged it myself and since I am the only one that maintains it not sure how that happened. So I plugged it in to an open slot and now have power to the idle solenoid but no action from the solenoid. I guess the two plugs by the tranny are what Brown explained and did well. Tried activating the idle solenoid with a/c on also no results. So does the idle solenoid works without a/c being turned on?

[brown7373]

The solenoid is only supposed to work when the compressor comes on. When the A/C is on, it puts a load on the engine and slightly lowers the engine idle speed. It is supposed to be adjusted so it pushed the carb linkage slightly and maintains the same speed as when the A/C is off. The solenoid rod is turned in or out with a wrench to adjust the idle speed when it is energized.

I had one of these on a 69 Corvette with A/C and it worked perfectly. It got it's power from the compressor wiring.

[Hubscrub]

the solenoid for ac is to jump the idle while compressor is running to make up for the lower idle, i have on my car is a one wire (hot) to test just jump it to the battery see if it pops out. i have wired them to a switch before to jump the idle up when i wanted before.

Do you have power brakes? if your idle problem with power brakes applied i say you have a vacuum leak since the booster uses vacuum.

[SS Tim]

Without pictures and an accurate description of the truck it is hard to nail down the exact setup your truck had new. But it goes to reason that by 72 it was the same as a Chevrolet. If you have a 1500 it had a TCS system and used an idle solenoid as an anti-dieseling measure due to the retarded spark timing. Take a look at the factory manuals and determine what you have/had, not just guessing what you have and why. This is from the 72 Chevy manual (EMISSION CONTROL SYSTEMS 6T-7) is a start. You can even download a copy of the manual.
But in your case I'd suggest buying a correct 72 GMC 1500-3500 factory service manual. IIRC Faxon www.faxonautoliterature.com (and others) should have both CD and paper copies.

Remember its an old truck with some unknown history to you. You can't just leave off parts of systems and expect everything to go on as normal. If you make changes like removing a TCS system you need to address everything it controlled.

* VIN/Model Decoders
* Power Team Charts (engine/transmission/gear ratio)
* Post Your Pickup SPID Blazer SPID Suburban/Panel SPID
* RTFM ... Read The Factory Manuals... download 'em here

[tk1251k]

Originally Posted by Hubscrub

the solenoid for ac is to jump the idle while compressor is running to make up for the lower idle, i have on my car is a one wire (hot) to test just jump it to the battery see if it pops out. i have wired them to a switch before to jump the idle up when i wanted before.

Do you have power brakes? if your idle problem with power brakes applied i say you have a vacuum leak since the booster uses vacuum.

It does have power brakes. It is a Sierra Grande model GMC. Have noticed brake light on in recent week but not fluid loss assume its air in the line somewhere but you may be onto something here as the idle goes. I will check it out today. Got power to the idle solenoid but plunger not activating so it must be bad. Hot end was traced to fuse panel under dash. I just pugged inot an open slot to get power with switch on.