Quadrajet, high idle with warm engine

[kikkegek]

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]

Anyone?

[1425956]

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

[edge]

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]

LPG missed that, I see now.

[tucsonjwt]

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]

Check the Throttle return springs.

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

[kikkegek]

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]

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]

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

[kikkegek]

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]

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]

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

[C-10 simplex]

EDITED: i didn't read carefully your response.

[Corts60]

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]

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

[Corts60]

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]

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]

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]

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]

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]

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]

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]

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

[CaptRMW]

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...