Idle issue after connecting ac vacuum

erv1994 · Oct 30, 2024

A little back story. My ac vacuum line was never connected when I purchased my truck. I decided to disconnect the vacuum line from my Cruise control servo and use that line to my ac vacuum line since I don’t use Cruise control. To my surprise all my ac controls worked but now my truck is idling rough(much lower than usual) and smells like it’s running rich. This is even with my ac is turned off. I don’t believe I have a vacuum leak since all my ac controls and vents work.

Can the amount of vacuum that is pulled from my ac system (even though it’s off) cause my idle to drop and truck to run rich?

YakkoWarner · Oct 30, 2024

erv1994 said:
A little back story. My ac vacuum line was never connected when I purchased my truck. I decided to disconnect the vacuum line from my Cruise control servo and use that line to my ac vacuum line since I don’t use Cruise control. To my surprise all my ac controls worked but now my truck is idling rough(much lower than usual) and smells like it’s running rich. This is even with my ac is turned off. I don’t believe I have a vacuum leak since all my ac controls and vents work.

Can the amount of vacuum that is pulled from my ac system (even though it’s off) cause my idle to drop and truck to run rich?

Normally a vacuum leak will make it go lean, not rich. On a carb setup a vacuum leak can cause idle to drop (on TBI it would more likely go high).

You can test to see if your controls are leaking vacuum or not - use a hand held vacuum pump and draw some vacuum on the line going to the controls. With the controls OFF it should remain pretty constant - if it leaks down quickly your controls have a small vacuum leak which could impact the running.

The other point is that the CC may be pulling vacuum from a different place on the intake. If it were me I'd find where the climate controls originally connected and run a vacuum line from there as originally designed, then see how the engine reacts. If the controls were never connected, there may be an open port that was compensated for by adjusting the carb to run richer, and now with that port closed its too rich.

Ricko1966 · Oct 30, 2024

IDK what truck,what engine,or what induction you are running,but as @YakkoWarner stated you need to pull vacuum on the ac control and see ifbit holds vacuum. And your question about the amount of vacuum pulled affecting idle or mixture no,that is not a possibility in a system without a leak,if you have a leak,yes that could affect idle and mixture. If you don't have enough vacuum to hold whatever power enrichment system your carbureator uses closed,it will go rich. If you are holding enough vacuum to keep the map sensor happy on TBI it will go rich.

erv1994 · Oct 30, 2024

Ricko1966 said:
IDK what truck,what engine,or what induction you are running,but as @YakkoWarner stated you need to pull vacuum on the ac control and see ifbit holds vacuum. And your question about the amount of vacuum pulled affecting idle or mixture no,that is not a possibility in a system without a leak,if you have a leak,yes that could affect idle and mixture. If you don't have enough vacuum to hold whatever power enrichment system your carbureator uses closed,it will go rich. If you are holding enough vacuum to keep the map sensor happy on TBI it will go rich.

Sorry it’s 1986 c10 305 5.0

Ricko1966 · Oct 31, 2024

erv1994 said:
Sorry it’s 1986 c10 305
49 states or California emissions

Ricko1966 · Oct 31, 2024

I'm guessing 49 states. Still has a qjet carbureator? Put a vacuum gauge on manifold vacuum,check your reading,disconnect and plug the AC vacuum line see if the reading is the same,it should be.

erv1994 · Nov 7, 2024

Ricko1966 said:
I'm guessing 49 states. Still has a qjet carbureator? Put a vacuum gauge on manifold vacuum,check your reading,disconnect and plug the AC vacuum line see if the reading is the same,it should be.

It’s a CA truck. I decided to undo what I had done to stop the rough idle, So i disconnected the ac vacuum line and reconnected the cc servo as it originally was but now the rough idle remains. Im at a loss. I’ve attached some pics. I believe I have an electric quadrajet carb. Electric choke cable was a bit melted but it was still activating my choke. Could it be possible that the moment I connected my ac vacuum line it threw off my carb mixture and/or timing off? Engine Vacuum reads Normal as well. Any help is appreciated. Thank you

Idle issue after connecting ac vacuum

erv1994

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