Remove the TPS from the T/b and manually adjust it through its range to see if it will give 0.5 volts. If it does, then your problem is a vacuum leak or a misadjusted throttle cable. EGR leaking?
Look at the throttle plates, there should be almost no clearance between the blades and the bore.
If all else fails, then bring engine to operating temp, turn off, place ecm in diag mode(paper clip between pins A & B of ALDL connector), turn key to IGN on, no start. This tells the ecm to activate all devices, EGR solenoid and runs out IAC. Turn key off,
unplug IAC, remove wire between A & b of ALDL connector. Start engine, base idle should be around 500-550 rpms, with everything else correct, TPS, engine coolant hot, oil pressure okay, no vacuum leaks, etc.
If too high, remove seal covering adjustment screw and adjust rpm to this level. Turn ign off, plug in IAC, remove codes, and see what happens. This should take care of it.
A couple more items, did this happen all of a sudden? Make sure brake master vacuum booster does not have a hole in it, large vacuum leak.
Check everything else before making base idle adjustment.
[This message has been edited by Everett#2390 (edited 05-22-2002).]