AC idle up vacuum routing (1 Viewer)

cheezypoof

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Desmogged '86 2F, new truck to me. I'm troubleshooting a fast idle (1400-1500rpm) that starts once the engine is warmed up (cold idle with and without choke is fine). After reading a few threads here I decided to first check the AC idle up system.

The way it's setup now, the vacuum ports on the idle up solenoid (driver's side fender) look like this:
idle up solenoid marked_LI.jpg

idle up upper port destination_LI.jpg


B1 to brake booster B2. R1 to brake booster plug (I think that's what that is?) R2

Meanwhile the idle up pot is connected to the VCV (that can't be right?):
idle up pot to vcv_LI.jpg


My best guess is B1 should go to the idle up pot (G1), in which case what gets connected to G2 and B2?

I failed to decipher the vacuum diagrams I found here (for smogged and desmogged setups) :(
 

DrRock

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Check that your idle up and choke screws aren’t over riding your idle speed screw. There was another recent thread where a member had a similar issue. I also struggled with this when adjusting my mixture but all is good now. As far as your vacuum lines go, I’ll shoot a picture later and add it to this thread.
 
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OSS

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Connect the vac hose that's labeled R1 on the solenoid directly to the carb AC idle up vacuum actuator.

To rule out if the AC idle up vacuum diaphragm is causing the fast idle, just disconnect it and plug the hose.

There's a lot of weird vacuum hose connections going on in your picture.
 

Gretsch

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Just for reference on AC idle up:

ac idle up.JPG


I prolly wouldn't rely on what PO did based on your photos. Get one of the available desmog guides and double check where things should be.

HTH
 

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cheezypoof

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Check that your idle up and choke screws aren’t over riding your idle speed screw. There was another recent thread where a member had a similar issue. I also struggled with this when adjusting my mixture but all is good now. As far as your vacuum lines go, I’ll shoot a picture later and add it to this thread.

I think I just found that thread, will get in there and lube up the linkages / check if those two are overriding idle speed. Thanks!
 

cheezypoof

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Don’t lube per say. Best to scour w/ green scotchbrite. Any lube/grease will attract grit like a magnet.

Good advice, thanks. I was planning to go at it with carb cleaner, also to hunt down potential vacuum leaks. My understanding is carb cleaner has some lubricant in there.

Per OSS's comment above it appears I need to look at more than just the idle up routing...
 

cheezypoof

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None of the vac hoses are routed correctly. Appears to be completely random connections.

Start from scratch, using these sources:
Emissions FSM

Desmog schematic

Desmog component layout

LOL not even just one? 😂

I mean, that takes some real effort. Just shows how tough these motors are, this one doesn't seem to run that bad despite this. I've got some work to do...

Thank you once again everyone
 

DrRock

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4C4A459A-7BD1-4643-9B30-B2B0548AC424.jpeg
Here’s the photo from my engine bay. Since your engine is “desmogged“ in a rather creative fashion, I‘ve included the Desmog guide that was kindly assembled by another member. Let us know if you need help.

EDIT: Didn’t realize Gretsch already included the guide.
 

cheezypoof

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View attachment 2490001Here’s the photo from my engine bay. Since your engine is “desmogged“ in a rather creative fashion, I‘ve included the Desmog guide that was kindly assembled by another member. Let us know if you need help.

EDIT: Didn’t realize Gretsch already included the guide.

Thanks DrRock. I have the desmog guide printed out, on my third or fourth read thru. It's a lifesaver. Also have the FSM and some other resources I found here. Now awaiting arrival of new silicone hose and plan to re-do this from scratch next weekend. I'm betting you'll see a frantic thread sometime around then haha.
 

DrRock

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Dr rock, the carb AC idle up is not connected to AC idle up VSV on the fender. Maybe intentional?
Hello Jim, partially intentional, thank you for the feedback! When I read the de smog document I missed the last note from you stating the AC idle up gets its vacuum source from the Brake booster fitting. Since I didn’t want to just leave it open I put it on the air cleaner lid until I got it sorted, which now I do!

I got all of your parts installed too, thanks.

Cheers, James
 

cheezypoof

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Finally had some time to tackle this

Thanks to everyone who helped here, and especially to @Borick for his invaluable desmog guide.

As noted above by @OSS and
@FJ40Jim the original setup was creative, probably less than half of the lines were routed correctly. Ripped everything out and replaced with fresh McMaster Carr lines. voila, idle issues appear to be corrected! Even the AC idle up works the way it should.

I discovered why they had capped the main diaphragm on the distributor vacuum, the port is clogged with fine grains of rust. Currently using the HAC port (outer diaphragm) until I can replace the part.

I disabled HIC/HAI for now but will hook it back up to test function.

Adjusted the idle speed screw down to 750 and it appears to be stable and happy there. Still need to do a lean drop but reaching that mixture screw looks like a royal PITA... figured I'd save some fun for the upcoming long weekend.
 

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