its throwing the code because somewhere its letting in more air causing the ISC to "malfunction" and the computer throwing the code. just first like silver said do a boost leak test. make a tester or buy one...i think boostpro.net makes one with a pressure gauge built-in so you don't gotta run inside to car to look at your boost gauge so you dont over pressurize the system.

 

I would say its the fiav. They make a block off plate which lets you keep your ISC motor. As the engine warms up its supposed to close, not letting as much air bypass the throttle plate (its a simple thermostat). Yours seems stuck open, letting air continue to bypass the throttle. You might want to check the throttle shaft seals as well. I had this same problem, but to fix it I went a little over board. I replaced the throttle body gaskets, the BISS screw and o-ring, the throttle shaft seals, and put in the FIAV block off plate. My idle is perfect now. however, without the FIAV, its a little choppy if its a cold morning. If its warm though its perfect

 

Thank you to everybody that replied, you have given me some stuff to do now all I need to do is go out and do it.

 

lol have fun....it took me a month before by the time i researched the causes and how to fix it, but atleast you got a few things to do.

*remember, go from simple solutions (which are usually free) and then work your way up tothing that can cause you moneythat can be causing it.