SO i have a 2009 Suzuki gs500f, i bought it used with the idle issue. I thought it would be an easy fix, holy CRAP i was wrong. I took it to a garage to get worked on and see if they could repair it. Here's what they told me they have done and i have done. I have bought new spark plugs and put non-ethanol gas in it. They tuned the carbs, adjusted and checked the valves, and check for air leaks in multiple places, made sure all the gas lines were clear, made sure the clutch and throttle cables were loose and not hung up, and the bike still idles at 3k. The idle adjustment screw does almost nothing except make it higher. Any idea's?

Check if choke system is working properly on the carbs when you pull the lever on the handlebar.