MONTE CARLO High Idle won't kick down

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1988SS

Apprentice
May 9, 2020
57
11
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Need a little more help. 1988 Monte Carlo SS with all original emissions and ECM (ccc) stuff.

After start-up and warm-up....the high idle sometimes won't kick down. Sometimes it will come down if I pop the peddle hard....other times it just comes down on it's own after driving a bit.

I hit the linkage with some cleaner but didn't seem to help. Any thoughts?

I've ordered a book on the Quadrajet (with ccc info) so I can be a bit more knowledgeable with this carb.

Thanks for any input.
 

pagrunt

Geezer
Sep 14, 2014
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Elderton, Pa
Quick & simple check, is the choke and/or linkage sticking? Might be as simple as a cleaning. Make sure all the mechanical linkage is clean with nothing binding.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
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Galaxy far far away
Check for sticking choke and linkage. Also be sure the electric choke is getting power and heating up.
 
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g0thiac

G-Body Guru
Sep 6, 2020
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Need a little more help. 1988 Monte Carlo SS with all original emissions and ECM (ccc) stuff.

After start-up and warm-up....the high idle sometimes won't kick down. Sometimes it will come down if I pop the peddle hard....other times it just comes down on it's own after driving a bit.

I hit the linkage with some cleaner but didn't seem to help. Any thoughts?

I've ordered a book on the Quadrajet (with ccc info) so I can be a bit more knowledgeable with this carb.

Thanks for any input.
3. things to check.

1. Vacuum leaks.

2. See the voltage you are getting at the choke.

3. Lastly see if the vacuum diaphragm, moves correctly, because in my 1988 Caprice I had that happen too.
 
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1988SS

Apprentice
May 9, 2020
57
11
8
I attached a long hose to this port of the pull-off.....I sucked on the end of the hose, but did not get any movement. Does this confirm a bad diaphragm tank?
 

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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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I attached a long hose to this port of the pull-off.....I sucked on the end of the hose, but did not get any movement. Does this confirm a bad diaphragm tank?
Normal. There's likely a ported hole in it keeping you from sucking that in the way you're doing it. Regardless, it's a 99.999% chance it doesn't have anything to do with your issue. There's a primary pulloff on the front which is much more influential. Remove the rubber hose and draw a vacuum on it. If it moves and forces the primary choke plate open, it's ok. But if it doesn't move with vacuum applied, it's toast. I'd also run through the linkage cleaning and operation again to make sure something isn't hanging up.

17085554 reassemble 112.JPG



If you find out you need one, then it's GM p/n 17067800.

 
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69hurstolds

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Jan 2, 2006
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Agree with the checking of the electric choke heatup. Ensure voltage is getting to the choke.
 
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ELCAM

Royal Smart Person
Jun 19, 2021
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The front diaphragm can have a delay and the rear one is certain to, keep that in mind it might not be all or nothing when you put vacuum to them.

I would pull that red vacuum cap in the background of your pic and use it to test. Make sure the engine is warm enough the vacuum leak will not kill it. Put your finger over it to test it. Might have to watch the vacuum cannisters as it warms up to see total movement.

Dual Delay Choke QJ.jpg
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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The factory front vacuum pulloff on Montes do not appear to have a delay port on them. I know for sure Oldsmobile 307s don't. So when you apply vacuum it should go. Besides, when the engine starts cold, it MUST move to pull the choke open slightly from full shut, approx. 1/8 inch or so.

Again, that rear vacuum break you've got in your picture is a waste of time. It doesn't have anything to do with your issue.

Is your carb a 17087129 carburetor? I was under the assumption that they didn't even use a secondary pulloff for 87-88. In fact, there's no replacement part number in the parts information for secondary pulloffs for 88 monte ss carb. I'm thinking someone's messed around with your carb. I see screws on your choke cover where there should be rivets.

Check the number on your carb. Driver side rear. There's a pad with some numbers stamped sideways on it. Take a pic or tell us if that number is on it. Because if it isn't a 7129, you've got a different carb on that puppy. I's actually an 87 part number, but they carried over the same carb from 87 to 88.
 
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