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I have a 89 pickup, 22R 4 cylinder, 2 barrel carb, manual transmission. The problem is the engine is acting crazy. It idles extremely hard and shakes violently, also it jumps up and down between 600 to 800 rpm, it wont hold the 700rpm as specified. I've checked the vacuum lines, air cleaner, pcv valve, ignition timing, thermostatic air cleaner and sprayed the carb with cleaner. I also replaced the EGR valve. When I start the engine it runs good, then after the fast idle cam disengages it goes crazy. When I accelerate its fine but when I let off the gas it jumps around again. Does anyone know what I can do?
 

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One with the farce
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3,139 Posts
I would try a different carb, just to be sure it's not that.
 

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YOTA Master
'93 2wd P/U
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2,434 Posts
This kind of situation is very hard to pin down by a text description. What you describe may be completely different from how I would describe the exact same problem. This is where first hand observation is benificial.

A couple of common problems with those carburetors include:

Sticking chokes and or linkage. This can be remedied by thoroughly cleaning the choke, chokeshaft where it goes through the carb top, and the linkage on the side of the carb that actuates the fast idle cam. I've seen many instances of others claiming to have cleaned these parts that have not done a good enough job and continuing to have problems.

Leaking Auxillary Accelerator Pump (AAP) Diaphram. On the passenger side of the carburetor is a small cover with 3 screws holding it on and a single vacuum hose going to it. Remove the vacuum hose and see if there is gasoline in it. If there is then the diaphram is leaking and you will have to replace it. Also if it has been leaking long enough it may have damaged the thermostatic vacuum swithing valve (TVSV).

One other problem I've seen is plugged up idle circuits that do not allow enough fuel through that portion of the carburetor. When this happens someone usually tries to make adjustments to compensate for this and the throttle ends up being to far open causing fuel to be pulled through the main circuit at too low of engine speed resulting in an idle that hunts around much as you have described. This condition is evident if at idle fuel can be seen dripping inside of the venturis when looking down the carburetor throat. This is likely to be accompanied by a "spitting" sound.

Keep in mind that you have a pretty old truck and there ultimately are many things that could be wrong. These are just common problems I've encountered.
 
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