96Z28 code P0507 idle too fast

car is a 96Z28, auto, headers, The code is P0507 (Idle Control System RPM Higher Than Expected). Ok this has been going on for some time now. The only way I could get the code off was to turn the idle screw down to lower RPM (I know you should not do this), this took care of the problem but my idle was up/down not steady, so I have done all the following, I changed the IAC, TPS and changed the rubber elbow(small leak), changed TB and still no change. Computer has been changed, no change. smoke tested for vaccum leaks, new TB gaskets, injectors cleaned. Only thing I know to do now is to get bryan at pcmforless to program out the code and he said he could. anybody got any help before I reprogram the computer. the car runs great and the idle is better but the code is still there, and I have cleared it several times.

Does it have an EGR that's stuck half open and throwing the idle out?
Does it surge ? I doubt the pcm programming is the problem, I'd recheck the basics! It might require a scan tool to relearn the base idle before proper diag can be successful, Might be an ign timing problem as well!

the egr is still there but is programed out, the exhaust pipe connection between the intake and header is blocked off and sealed. but the idle problem started before we changed headers, the RPM is only a little high now, I turned the idle screw down again, but the idle is not smooth, 50 to 75 rpms up and down, hanging around 750 which is high but not a bad idle. runs great, gas mileage about 14 around town. I read somwhere that you can reset IAC by pressing down the pedal a little and holding it there, then crank the car, let off the pedal for 5 seconds, turn off, wait for 10 sec. then restart, this seemed to help, but I'll have to drive it for another day to make sure. have you hear about this for the IAC.

no! Maybe you have an exhaust leak near the 02 sensor(s) and it's throwing the fuel curve out of whack!

new 02 sensors, but I will check for leak
thanks for the help and may my have a Happy Thanksgiving
will get back to you later

i don't know why it cleared up after i did the following, i drilled the holes out on the TPS so as to move in any direction, will i turned back counterclock wise and restarted the car, drove awhile the code still there and idle a little rough, i turned the idle screw up a little to smooth out the ide, still had code. ok i took the TB off and removed the IAC and cleaned again, i took some 300grit wet/dry black sand paper , a very small piece , with my little finger i was able to get the paper into the IAC hole and turned it around and around, making the seat smooth which it was not, blowed out with air and carb cleaned, reset the IAC again and put back in, did the reset by starting the car with throttle part open then removed my foot from pedal counter 5 sec, shut off for 10 sec restarted, the idle was smoother, drove for a while still code, the last thing i did was to loosen the TPS again and only turned a little clock wise then tigthen back down, started the car, the code left and has not come back on, good idle, runs good, go figure, it don't smake sense, but it worked.

FYI for others who get this code - http://www.obd-codes.com/p0507