88 1500 5.0 throttle sticking closed

Greg S Meier

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The butterflies are sticking when its running cause the vacuum is pulling it further shut. Take the plug out of idle screw and give it 1/8-1/4 turn and i bet it fixes it
Turn. Clockwise or counter clockwise sir?
 

Pinger

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Clockwise.

What is the purpose of that screw (given IAV controls idle)? Is just to prevent the butterfly edges from stopping against the throttle body?
 

Schurkey

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The screw sets minimum idle speed, the engine should idle even if the IAC gets completely shut. So don't just "turn the screw" randomly. You need to set minimum idle speed as directed in the service manual.

Yes, primarily to prevent the throttle plates from jamming in the throttle bores.

I've seen carburetors that have extra-thick, extra-rigid throttle plates with machined taper on the edges of the plate, to fit precisely into the throttle bores because those throttles are intended to close completely, but not "stick" in the bores.
 
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someotherguy

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Fix what's wrong before you go dorking with the adjustment screws. Sure, you can tweak an adjustment to hide the real issue, but if you ever want it to run factory-perfect again, don't.
Agreed. Almost never, ever a reason to touch that screw. That's why the factory hid it behind a plug that was not meant to be removed.

Richard
 

Pinger

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That screw though, should be in contact with the throttle mechanism (zero clearance) - and be the absolute stop for the butterfly?
 

bowtie-72

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Agreed. Almost never, ever a reason to touch that screw. That's why the factory hid it behind a plug that was not meant to be removed.

Richard
X2 on what these guys are saying. JUST CLEAN YOUR THROTTLE BODY FIRST. This is normal PM maintenance anyway. Even if it isn’t your problem, it will give you a place to start. I have seen a few trucks with the exact same problem you have and they were all fixed with a simple spray down of the throttle body. You will use about 25% of the can so you will still have enough left over to do it a couple more times.
 

PlayingWithTBI

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That screw though, should be in contact with the throttle mechanism (zero clearance) - and be the absolute stop for the butterfly?
Yes, that's why you set the base idle with IAC closed. GM did it with the bone stock engine but, if you add any goodies, it needs to be done again. But, as I said in post #4 the OP needs to look at the throttle shaft for slop/wear which can also cause it to jamb under vacuum.
 

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badco

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Ckockwise. And i learned this from a gm service bulletin when i worked at dealership in late 90s. The shafts wear and get clearance in them causing them to get aginst the throttle body. The bulletin had us use a real narrow .005 feeler gauge and set a air gap. So wouldn't that be fixing the problem? Listen to whoever you want on it and spend all you want it yours not anyone elses.
 
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