1992 Isuzu P'up

My 2.3 ltr engine is revving high and it just recently started doing this. I tried adjusting the throttle rest adjustment screw but it did nothing for
it. I should note that the carburetor has had a moderate miss to it for some time now. I took the filter element and housing off and it still revs high. I checked for proper connections of all vaccum lines. I have an aftermarket air conditioner that was installed in 2000. The engine has 111,000 miles on it and does not smoke.
Can anyone offer some advice.
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