High idle on 98 chevy 5.7. changed Intake manifold & gasket,TPS, IAC Valve, 02 sensor, map sensor. plugs good, wires good, New cap & rotor. no vacum leak. Picked out a identical PCM but need to get it flashed for 125 on monday. Any thoughts.

when you put distributor back in most likely off a tooth

I'LL TRY, GOOD TO SEE SOMEONE TRY AT LEAST ! IDLE SEEMS HIGH, BACK TO BASICS !!!!!! THE AIR & FUEL FILTERS NEED REPLACED, SPARK PLUG WIRES, YOU FORGOT THEM !!! DISTRIBUTOR CAP & ROTOR, YOU FORGOT THEM !!! THESE ARE AS IMPORTANT AS THE AIR WE BREATHE !!!!! VACUUM LEAKS, CHECK ALL VACUMM LINES, THOROUGHLY ! THIS LINE COMING OUT OF THE TRANSAXLE PORTION OF THE INTAKE MANIFOLD ?????????????????/ YOUR NEED TO REPLACE WHATEVER IT IS, WHAT KIND OF LINE ? METAL, RUBBER , WIRE ??? MOVING ON, GOOD YOU REPLACED THE OXYGEN SENSOR, & IDLE AIR VALVE, & TPS, RECHECK TPS, IS IT LOOSE, ALSO TIGHTEN THROTTLEBODY BOLTS, THE ONES THAT HOLD IT DOWN. SO, CHANGE YOUR FILTERS,WIRES, ETC., MENTIONED ABOVE, CAP & ROTOR, ETC.,ETC.,.........GO FROM THERE, SEE HOW THAT WORKS

Have u checked the cadeletic converter. It can do funny things

If you have the 5.0 liter engine or the 5.8 litre there was a problem with the upper intake manifold gasket being cracked and sucked into the intake causing a vacuum leak and the result was high idle. Also a leaking egr will sometimes cause high idle.

TPS probably not cause surging idle. Could be IAC motor, could be MAF sensor. If you dont have a check engine light I would be thinking IAC motor.

High idle
Changed IAC still the same, shown on scanner IAC 50-60 %, if it set to 40% the Idle is ok. What cause the PCM to set IAC too high? Is any one know?

sounds like the idle air is gone

check and clean ur egr valve possible carboned up -clean valve with carb cleaner and check valve movement

massair frow sensor

My problem was solved when I repaired my 4 wd activation dash switch. The switch was contacting on 2WD & 4HI at the same time. The front differential activation is vacuum activated possibly creating a tug of war that didn't actually engage it but drained off vacuum from the engine? A theory at best but stumbbled across it because I knew the switch wasn't working properly I repaired it and low and behold rough idle disappeared and all is good for 3 weeks running.