Quadrajet, high idle with warm engine - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kikkegek · 04-15-2011, 04:35 PM

I have an annoying problem.

Whe my engine is cold, no problems It idles nicely at about 500-700rpm. And the throttle return nicely all the way.

But after some driving and the engine warmed up, the throttle does not fully return to the idle position all the way by itself. I need to pull the pedal up by hand or foot or need to kick the throttle once...only then with a warm engine it will rev down from the 1000-1100 rpm to 500-700...

I already checked if it is the cable, unhooked it and tested by hand...slowly releasing the throttle linkage and quickly releasing the throttle linkage...when I release it slowly...it will not return for about I think only 1-2 mm....wich is only a lttle...but causing the annoyingly high wining of the engine....

and only when the engine is warmed up ....please help

btw..its a Rochester Quadrajet

some pics to help and the serial to identify...

any ideas why it idles high when warmed up?

**N2TRUX** · 04-16-2011, 10:59 AM

Anyone?

1425956 · 04-16-2011, 11:33 AM

Looks like you are running LPG? If so, I would check the vacuum to the LPG regulator.

edge · 04-16-2011, 11:38 AM

Sounded like the cable till I read that you tested the cable movement by hand. I still think it is the cable sticking. But you havent said anything the choke.

edge · 04-16-2011, 11:40 AM

LPG missed that, I see now.

tucsonjwt · 04-16-2011, 11:57 AM

My Qjet does the same thing, but the engine revs only slightly high at idle - still annoying. I jab the accelerator and the idle returns to normal. I have no LP system. I have a manual choke so I know the choke is fully open when the engine is warm. The throttle bracket can be manually moved back at idle to return engine revs to desired normal level (equivalent to jabbing the accelerator pedal). Maybe it was the "professional" rebuild I had done on the carb.

*C-10 simplex* · 04-16-2011, 12:18 PM

Check the Throttle return springs.

What type of carpet do you have? Or do you have a rubber mat on the floor?

kikkegek · 04-16-2011, 01:31 PM

thanks guys...

The LPG systems has no vacuum connection. check.

the carb has high idle also with the cable of. So its not the cable.

yes, checked the return springs. Its a double spring and the tension is more then enough.

why the question on the carpet? we do have rubber mats on the carpet.

when the engine is warm, I notice that the last bit of the throttle linkage, just before idle, doesnt return by itself, when you let go ot the throttle slowly. When you release the throttle suddenly, theres no problem.

hpe you guys can help me!

tucsonjwt · 04-16-2011, 04:19 PM

On mine, a stronger throttle spring does not help. You have to manually pull back on the throttle linkage a lot, with a quick motion, which releases the associated linkage on the carburetor which is hanging it up (I think). I know it does not make sense, but that is the condition I have.

geezer#99 · 04-16-2011, 04:25 PM

Put your spring in front of the carb. Pulling forward should cure it.

kikkegek · 04-16-2011, 04:39 PM

Quote:

Originally Posted by geezer#99

Put your spring in front of the carb. Pulling forward should cure it.

I already tried one spring, didnt help. Maybe I'll make a bracket en see if it helps...

I dont have any knowlegde of the inside of the carb, but could it not be rubbing against something inside?

one spring facing forward with a tie-wrap! (srry!)

tucsonjwt · 04-16-2011, 06:55 PM

I don't think a spring in front will help. I can push forward as hard as possible on the throttle bracket and truck won't idle down. It requires a sharp motion to the rear to release whatever is hanging up the throttle bracket. All of the other linkage associated with the throttle bracket is operating freely and loose, so I don't know what it could be. The throttle bracket itself seems to be "catching" on something.

geezer#99 · 04-16-2011, 09:12 PM

Any play in your primary throttle shaft from side to side. Could be primary plate is hanging up a bit.

*C-10 simplex* · 04-16-2011, 10:07 PM

EDITED: i didn't read carefully your response.

**Corts60** · 04-16-2011, 11:23 PM

This is your culprit:

There is a step on that component that is keeping your idle raised. In other words, with your engine running, take one hand move the throttle to just off idle, and then push that lever down. Let go of the throttle and your idle should be whatever your set-screw is set at.

If that works, you need to adjust that lever with a screw that is attached to it.

tucsonjwt · 04-16-2011, 11:32 PM

I will try that. Does the vacuum solenoid have to be removed to access the adjustment screw?

**Corts60** · 04-17-2011, 12:36 AM

Quote:

Originally Posted by tucsonjwt

I will try that. Does the vacuum solenoid have to be removed to access the adjustment screw?

Nope. That component is actually called a choke pull-off. The adjustment screw is a pain, it is kind of pointed upwards and you need to use a stubby screwdriver.

kikkegek · 04-17-2011, 09:41 AM

he guys, thanks for the tips.

I made a picture of my passenger side of the carb. Can you point out what you mean in this pic?

**Corts60** · 04-17-2011, 11:35 AM

I can't see it in your picture, but that lever I circled above is called the fast idle cam. I couldn't remember the name last night to save my life. I am not seeing it on your carb because of the electric choke, but there has to be some kind of fast idle cam on that side of the carb. That is gives the high idle during warm up. See if you can find it and the adjustment screw for it.

kikkegek · 04-17-2011, 12:58 PM

hi Corts60...thanks for your reply, but I dont have high idle problem during warm up, but when the engine is warmed up....

when is is still warming up, its just fine..but when it is warm, it idles a little higher

**Corts60** · 04-17-2011, 02:24 PM

Yes but that fast idle cam is more than likely what is keeping the idle high. If it is out of adjustment, it won't drop the idle back down even when you rap the throttle.
Posted via Mobile Device

kikkegek · 04-18-2011, 06:34 AM

Quote:

Originally Posted by Corts60

Yes but that fast idle cam is more than likely what is keeping the idle high. If it is out of adjustment, it won't drop the idle back down even when you rap the throttle.
Posted via Mobile Device

can you point out in my picture where I would find the fast idle cam?

kikkegek · 04-21-2011, 06:04 AM

can somebody point me out where I would find the fast idle cam on my carb? so
I can check this?

the thing is that in my case the idle DOES drop down when I kick the throttle gently...so it seems more that my setup is rubbing something somewhere when the engine is warmed up...I just cant find out what...any ideas?

JMac11 · 04-21-2011, 08:36 AM

The Green lever is fast idle linkage. Spritz that whole side with cleaner/wd 40.

CaptRMW · 04-21-2011, 08:49 AM

Quote:

Originally Posted by JMac11

The Green lever is fast idle linkage. Spritz that whole side with cleaner/wd 40.

JMAC 11 is exactly right and a good shot of Blaster or WD 40 on the SECONDARY shaft on "both sides" will likely cure your problem. You will need to give it a shot once in a while since Rochester didn't find a cure for this problem...

04-15-2011, 04:35 PM	#1
kikkegek Registered User Join Date: Aug 2010 Location: Netherlands, The Hague Posts: 1,518	Quadrajet, high idle with warm engine I have an annoying problem. Whe my engine is cold, no problems It idles nicely at about 500-700rpm. And the throttle return nicely all the way. But after some driving and the engine warmed up, the throttle does not fully return to the idle position all the way by itself. I need to pull the pedal up by hand or foot or need to kick the throttle once...only then with a warm engine it will rev down from the 1000-1100 rpm to 500-700... I already checked if it is the cable, unhooked it and tested by hand...slowly releasing the throttle linkage and quickly releasing the throttle linkage...when I release it slowly...it will not return for about I think only 1-2 mm....wich is only a lttle...but causing the annoyingly high wining of the engine.... and only when the engine is warmed up ....please help btw..its a Rochester Quadrajet some pics to help and the serial to identify... any ideas why it idles high when warmed up? __________________ My dreamride / project:1977 GMC C15 Suburban In storage: Monster - 1974 GMC Suburban 25hundred Sold : Chevrolet Suburban K20 Silverado 1986 Guide: real HID projectors for 4x6 headlights link: DIY LED TAILLIGHTS

04-16-2011, 10:59 AM	#2
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,021	Re: Quadrajet, high idle with warm engine Anyone? __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

04-16-2011, 11:33 AM	#3
1425956 Registered User Join Date: Mar 2011 Location: Joplin, MO Posts: 161	Re: Quadrajet, high idle with warm engine Looks like you are running LPG? If so, I would check the vacuum to the LPG regulator. __________________ Jeremy I have done so much, for so long, with so little, I can do anything with nothing! 1984 GMC Sierra Classic-1/2 ton-SWB (R.I.P.) 1986 GMC Suburban 3/4 ton 4x4 2014 GMC Sierra LTZ Z-71 Crew SWB Last edited by 1425956; 04-16-2011 at 11:35 AM. Reason: Added info

04-16-2011, 11:38 AM	#4
edge Registered User Join Date: Nov 2006 Location: ky Posts: 89	Re: Quadrajet, high idle with warm engine Sounded like the cable till I read that you tested the cable movement by hand. I still think it is the cable sticking. But you havent said anything the choke.

04-16-2011, 11:40 AM	#5
edge Registered User Join Date: Nov 2006 Location: ky Posts: 89	Re: Quadrajet, high idle with warm engine LPG missed that, I see now.

04-16-2011, 11:57 AM	#6
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: Quadrajet, high idle with warm engine My Qjet does the same thing, but the engine revs only slightly high at idle - still annoying. I jab the accelerator and the idle returns to normal. I have no LP system. I have a manual choke so I know the choke is fully open when the engine is warm. The throttle bracket can be manually moved back at idle to return engine revs to desired normal level (equivalent to jabbing the accelerator pedal). Maybe it was the "professional" rebuild I had done on the carb.

04-16-2011, 12:18 PM	#7
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: Quadrajet, high idle with warm engine Check the Throttle return springs. What type of carpet do you have? Or do you have a rubber mat on the floor?

04-16-2011, 01:31 PM	#8
kikkegek Registered User Join Date: Aug 2010 Location: Netherlands, The Hague Posts: 1,518	Re: Quadrajet, high idle with warm engine thanks guys... The LPG systems has no vacuum connection. check. the carb has high idle also with the cable of. So its not the cable. yes, checked the return springs. Its a double spring and the tension is more then enough. why the question on the carpet? we do have rubber mats on the carpet. when the engine is warm, I notice that the last bit of the throttle linkage, just before idle, doesnt return by itself, when you let go ot the throttle slowly. When you release the throttle suddenly, theres no problem. hpe you guys can help me! __________________ My dreamride / project:1977 GMC C15 Suburban In storage: Monster - 1974 GMC Suburban 25hundred Sold : Chevrolet Suburban K20 Silverado 1986 Guide: real HID projectors for 4x6 headlights link: DIY LED TAILLIGHTS

04-16-2011, 04:19 PM	#9
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: Quadrajet, high idle with warm engine On mine, a stronger throttle spring does not help. You have to manually pull back on the throttle linkage a lot, with a quick motion, which releases the associated linkage on the carburetor which is hanging it up (I think). I know it does not make sense, but that is the condition I have.

04-16-2011, 04:25 PM	#10
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,736	Re: Quadrajet, high idle with warm engine Put your spring in front of the carb. Pulling forward should cure it.

04-16-2011, 06:55 PM	#12
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: Quadrajet, high idle with warm engine I don't think a spring in front will help. I can push forward as hard as possible on the throttle bracket and truck won't idle down. It requires a sharp motion to the rear to release whatever is hanging up the throttle bracket. All of the other linkage associated with the throttle bracket is operating freely and loose, so I don't know what it could be. The throttle bracket itself seems to be "catching" on something.

04-16-2011, 09:12 PM	#13
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,736	Re: Quadrajet, high idle with warm engine Any play in your primary throttle shaft from side to side. Could be primary plate is hanging up a bit.

04-16-2011, 10:07 PM	#14
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: Quadrajet, high idle with warm engine EDITED: i didn't read carefully your response. Last edited by C-10 simplex; 04-16-2011 at 10:17 PM.

04-16-2011, 11:23 PM	#15
Corts60 Just here to tinker Join Date: Jun 2008 Location: Holland, MI Posts: 3,697	Re: Quadrajet, high idle with warm engine This is your culprit: There is a step on that component that is keeping your idle raised. In other words, with your engine running, take one hand move the throttle to just off idle, and then push that lever down. Let go of the throttle and your idle should be whatever your set-screw is set at. If that works, you need to adjust that lever with a screw that is attached to it. __________________ 78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/showthread.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 73 Chevy C20(Daily)http://67-72chevytrucks.com/vboard/s...d.php?t=852767 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(sold) Last edited by Corts60; 04-16-2011 at 11:31 PM.

04-16-2011, 11:32 PM	#16
tucsonjwt Registered User Join Date: Jul 2007 Location: Tucson, AZ Posts: 3,189	Re: Quadrajet, high idle with warm engine I will try that. Does the vacuum solenoid have to be removed to access the adjustment screw? Last edited by tucsonjwt; 04-16-2011 at 11:37 PM.



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04-17-2011, 09:41 AM	#18
kikkegek Registered User Join Date: Aug 2010 Location: Netherlands, The Hague Posts: 1,518	Re: Quadrajet, high idle with warm engine he guys, thanks for the tips. I made a picture of my passenger side of the carb. Can you point out what you mean in this pic? __________________ My dreamride / project:1977 GMC C15 Suburban In storage: Monster - 1974 GMC Suburban 25hundred Sold : Chevrolet Suburban K20 Silverado 1986 Guide: real HID projectors for 4x6 headlights link: DIY LED TAILLIGHTS

04-17-2011, 11:35 AM	#19
Corts60 Just here to tinker Join Date: Jun 2008 Location: Holland, MI Posts: 3,697	Re: Quadrajet, high idle with warm engine I can't see it in your picture, but that lever I circled above is called the fast idle cam. I couldn't remember the name last night to save my life. I am not seeing it on your carb because of the electric choke, but there has to be some kind of fast idle cam on that side of the carb. That is gives the high idle during warm up. See if you can find it and the adjustment screw for it. __________________ 78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/showthread.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 73 Chevy C20(Daily)http://67-72chevytrucks.com/vboard/s...d.php?t=852767 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(sold)

04-17-2011, 12:58 PM	#20
kikkegek Registered User Join Date: Aug 2010 Location: Netherlands, The Hague Posts: 1,518	Re: Quadrajet, high idle with warm engine hi Corts60...thanks for your reply, but I dont have high idle problem during warm up, but when the engine is warmed up.... when is is still warming up, its just fine..but when it is warm, it idles a little higher __________________ My dreamride / project:1977 GMC C15 Suburban In storage: Monster - 1974 GMC Suburban 25hundred Sold : Chevrolet Suburban K20 Silverado 1986 Guide: real HID projectors for 4x6 headlights link: DIY LED TAILLIGHTS

04-17-2011, 02:24 PM	#21
Corts60 Just here to tinker Join Date: Jun 2008 Location: Holland, MI Posts: 3,697	Re: Quadrajet, high idle with warm engine Yes but that fast idle cam is more than likely what is keeping the idle high. If it is out of adjustment, it won't drop the idle back down even when you rap the throttle. Posted via Mobile Device __________________ 78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/showthread.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 73 Chevy C20(Daily)http://67-72chevytrucks.com/vboard/s...d.php?t=852767 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(sold)

04-21-2011, 06:04 AM	#23
kikkegek Registered User Join Date: Aug 2010 Location: Netherlands, The Hague Posts: 1,518	Re: Quadrajet, high idle with warm engine can somebody point me out where I would find the fast idle cam on my carb? so I can check this? the thing is that in my case the idle DOES drop down when I kick the throttle gently...so it seems more that my setup is rubbing something somewhere when the engine is warmed up...I just cant find out what...any ideas? __________________ My dreamride / project:1977 GMC C15 Suburban In storage: Monster - 1974 GMC Suburban 25hundred Sold : Chevrolet Suburban K20 Silverado 1986 Guide: real HID projectors for 4x6 headlights link: DIY LED TAILLIGHTS

04-21-2011, 08:36 AM	#24
JMac11 Registered User Join Date: May 2005 Location: Tallahassee Fl Posts: 773	Re: Quadrajet, high idle with warm engine The Green lever is fast idle linkage. Spritz that whole side with cleaner/wd 40.

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