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Extreme high idle

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Mudslutk51984

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When my blazer starts up cold it’s very high idle I have to drop it in gear to get the idle to a reasonable level.. after a few minutes I hit the accelerator it drops to normal idle... what could be the issue? 1984 k5 4barrel quad
 
It’s probably just the choke, try hitting the throttle before you put it in gear to drop the idle.
 
That’s normal, especially when cold. Let it warm up a few minutes and the idle should slowly drop as it warms up. Unless your talking about an abnormally high idle at start up
 
Quadrajet ?..
I think there is a separate screw to set the fast idle when its on choke..
Also perhaps the secondary butterflies are hanging slightly open.
A leak at the base gasket to the intake can make it idle faster when its choked also..
 
It idles up to about what I’m guessing is 4000-4500 rpm.. not for sure on that, but where’s the choke idle screw
 
4000+ rpm is wide open throttle!..doubt its running that fast--probably more like 2500 rpm or less,it sounds faster but isn't..
If it were going 4000 rpm,and you put it in gear,you'd either have the tires start smoking or break something..automatics don't like high rpm neutral drops!..

I'd get this fixed ASAP,because one of the worst things you can do to an engine after a stone cold start is wind the piss out of it!...especially if its really cold,and you have fairly thick oil in it..you'll spin a rod bearing in a heartbeat letting it do this for long..
 
There is an adjustment for low idle and separate one for high idle. The "one pump" you do with the pedal before starting is to snap the choke shut and set the throttle on the high idle cam. First thing to do is go over the linkages and make sure everything moves freely. There are several of them on later-model Quadrajets with front and rear vacuum cans. When the throttle shafts get too worn it can make the performance inconsistent, but you unless it's too bad you can still bring idle down.

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Rule of thumb is that you won't need adjustments real far from the factory settings, but you never know what previous owners (or shops) have messed with trying to fix another problem. The difficulty with tuning cold starts is you only get 1 - maybe 2 - chances per day to test your adjustments.
 
You should be able to rotate the fast idle cam manually after the choke has opened to adjust the fast idle speed screw..
Been 20 years since I worked on a Q-jet,so my advice may not be accurate--I've forgotten a lot since then..
 
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