Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Q-jet won't idle when engine warms up

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Greg Kennedy:
Dear Cliff and friends:

So glad to have discovered this forum.

I love old Oldsmobile Toronados and my 1981, 307 gasoline engine with Quadrajet E4MC is giving me grief.

It ran like a top when I stored it last winter, and now it dies whenever the engine warms up now.

If I feather the gas pedal, it will keep running. Or if I tighten the low idle speed screw like crazy, it will keep idling roughly, but at around 1500 to 2000 RPM. I try to lower this and she dies.

If I step on the gas, it's smooth, but take my foot off the gas and she dies (unless I keep the idle screw tightened as above).

I've replaced the PCV valve, checked and cleaned the EGR valve. Checked vacuum hoses to the best of my ability. The baseplate gasket is new; I don't think I have a vacuum leak there. Sprayed some carb cleaner around it and it didn't affect the engine speed.

I did a rebuild about two years ago, but I confess at the time I didn't know much about how the idle circuit worked, and didn't run any wires, etc, down the idle tubes.

I have bought the special tool that let me play with the idle air mixture, trying two turns out, two and a half, three turns out, and now it's at three-and-a-half turns out on each side.

Bottom line .... could my problem be as simple as just removing the carb again -- and then making for damn sure the idle tubes are clean?

Or am I getting into a timing issue?

Remember, this is a car that never stalled before coming out of storage this spring .... and now it won't idle when warm.

I'm open, and very very grateful, for any expertise you folks can offer. I've already got a bald spot and don't want to pull out the hair I have left.  :D

I love the challenge of learning more about these amazing carbs, and I best order me a copy of Cliff's book straightaway here for future reference.

Thanks so much,
Greg

Greg Kennedy:
I just wanted to mention that my carb is not computer-controlled, if that matters,
Greg

carmantx:
Make sure your float is fully open when engine is warm.

429bbf:
welcome to chp. lets start simple . is it running out of fuel or does it act like its flooding.if it acts like its flooding the choke pulloff maybe bad . if its running out of fuel I wonder toward the idle tubes . fwiw ps carb no. would be nice

Greg Kennedy:
It's interesting you mention the choke pulloff -- if I use my finger to hold the choke valve when it's idling I can keep it running easily. So perhaps the idle rods aren't bunged up. The two vacuum breaks front and back seem to work fine and hold vacuum without fading. Thoughts?

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