my 86 z28 idles ridiculously high (2k) @ startup, and usually doesn't drop for a very long time (even after being warmed up and tapping the gas), although sometimes it will surprise me and drop back down to 500 or so. is this a computer issue, or does the carb just need adjusting? the carb is a quadrajet and i can't find any obvious adjustment screws. thanks in advance.

 

Welcome aboard.

There is an adjustment screw, but I suspect that isn't your problem. Since it will drop down to 500 RPMs once in awhile, that leads one to believe your choke isn't operating correctly. Either a sticky mechanism or the choke thermostat isn't warming properly would be my guess.

However, the 2000 RPMs is a little too high. The adjustment screw is on the passenger side of the carb, toward the bottom, facing the rear of the carb.
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Oh, the computer doesn't have anything to do with idle speed.

 

so, does the choke need cleaned, replaced,...a third option i'm unaware of? replacing it is simple, right? unhook one, hook up the other?

 

If it's the original, the choke thermostat will be pop-riveted on. They have to be drilled out. The new one will have to be attached with pop rivets or self-tapping screws.

The mechanism cleaning can be done from the outside, unless the inside works are also gummed up. How would you describe the overall condition of the carb?