How do you know if the Idle Air Control Valve is going bad?

Low or rough idle. Stalling when slowing to stop. But runs normally at highway speeds. Turn ac on-- does vehicle idle up. If not possibly dirty/faulty idle air control valve or dirty throttle plate.

It has been doing this since I tuned the engine. Checked auto parts store and a new one is about $60.00...they recommend a new replacement and not to try and clean the old one.

Honestly that's rather cheap compared to some. I would try cleaning first. But then again it's twenty seven years old. Personal experience with one in my 1985 z28. Took it off, cleaned it and then turned key on so I could see if the plunger moved. Damn thing (plunger) shot across the shed. Lol. Had to buy a new one anyway.

Replaced the air control valve today and the truck is running much better. Thanks for all the feedback folks!

Glad you got it going. Drive safe.

Another good tip is spray carb. cleaner around the base of the carb. I needed new gaskets but I had the carburetor off so it gets a good cleaning also