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Discussion Starter #1
I recently removed, cleaned, and replaced my plenum and the engine now idles so low after it has warmed up that it dies unless the accelerator is kept depressed.

Is it possible that I changed the length of the linkage (circled in the photo that was borrowed from another thread) and it is now causing it to idle too low? If that is a possibility, should it be shortened or lengthened to raise the idle? Or, is the length of the linkage not even a factor?

Thanks,

David
 

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But Mad North-Northwest
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When the throttle is closed it's against a screw stop. The linkage can't really change that to make it idle lower, so I doubt that's your problem.

Did you mess with anything else when you cleaned it? I'd start by making sure the TPS is adjusted and working properly. If that's okay I'd try just boosting the idle to spec via the idle adjustment bypass.
 

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I agree with Tom.

There is a throttle stop screw and an idle speed adjuster. The stop screw is not used to adjust the idle speed but rather to prevent the throttle plate (aka butterfly) from closing so tightly it jams in the throttle body. So, if it has been messed with (likely due to unknowing PO's), here's how I adjust idle speed. Unscrew it to allow the throttle plate to fully close. Then screw it in until the idle speed just barely increases (say 50 rpm using an accurate, digital tach - many timing lights have that function). Then lock the screw in position. Now use the idle speed adjuster to set the idle speed (900-1000 rpm). This is the item with the O-ring inside. Squeezing or unsqueezing the O-ring alters its ID and thus the amount of air allowed to pass through - thus affecting idle speed. An old O-ring will often get hard & take a set and thus resist 'adjustment'. Replace it with new, soft O-ring and it'll work correctly.
 

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^^....wot they said:)

not sure what effect it would have on the idle, but did you connect the little vacuum hoses back correctly on the plenum nipples?...they have different sized holes, so the correct hoses ideally need to go back where they came from.
https://www.alfabb.com/bb/forums/230371-post1.html
 

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Discussion Starter #5
^^....wot they said:)

not sure what effect it would have on the idle, but did you connect the little vacuum hoses back correctly on the plenum nipples?...they have different sized holes, so the correct hoses ideally need to go back where they came from.
https://www.alfabb.com/bb/forums/230371-post1.html
I did replace all of the vacuum hoses using a Hi-Performance store kit. As you say, the hoses can only go back a certain way and I took lots of pictures and made notes. I'll take a look at the TPS.

Thanks,

David
 

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Discussion Starter #6
I agree with Tom.

There is a throttle stop screw and an idle speed adjuster. The stop screw is not used to adjust the idle speed but rather to prevent the throttle plate (aka butterfly) from closing so tightly it jams in the throttle body. So, if it has been messed with (likely due to unknowing PO's), here's how I adjust idle speed. Unscrew it to allow the throttle plate to fully close. Then screw it in until the idle speed just barely increases (say 50 rpm using an accurate, digital tach - many timing lights have that function). Then lock the screw in position. Now use the idle speed adjuster to set the idle speed (900-1000 rpm). This is the item with the O-ring inside. Squeezing or unsqueezing the O-ring alters its ID and thus the amount of air allowed to pass through - thus affecting idle speed. An old O-ring will often get hard & take a set and thus resist 'adjustment'. Replace it with new, soft O-ring and it'll work correctly.
Thanks! I've read about the infamous o-ring. From what I can glean, McMaster Carr has them:

Viton 75 (fuel resistant) - size 201 3/16 ID 7/16 OD
or
BUNA N (fuel resistant) size 201 3/16 ID 7/16 OD

Thanks,

David
 
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