It is controlled by the ECU. I would check to make sure that you do not have any broken/cracked/disconnected vacuum lines and that there isn't a gasket leak between the throttle body and the intake manifold (somewhat common problem).
People will argue and say this won't work or you can't do that only the ecm adjusts idle speed, but trust me it does work I have done it to more than 1 tbi and it won't screw anything up. I have done it on my stock 4.3 tbi I have done it on my 5.7 jimmy /holley 670 tbi and lots of others,if you need it I have a pic of where the idle screw is hidden on the tbi's http://www.thirdgen.org/tpimod2
Last edited by xmradioguy; 10-29-2010 at 02:23 AM.