Within the last three weeks my idle has started pulsing/throbbing about 2x per second and about 50 to 100 rpm. Completely cleaned IAC and throttle body using new gasket. Replaced intake manifold gasket (very cracked/deteriorated) Checked for coked intake valves while in there (ok very clean). Checked plastic line to MAP sensor with a vacuum pump (ok holds vacuum, connection tight) Cleaned flame trap and hoses. Checked all vacuum hoses.
Ran EEC test to verify idle signal to computer, pass. Checked for codes in fuel and ignition computers, ok no codes. Started car and attempted to control idle by using finger over IAC vacuum port at manifold, can be controlled and idles smoothly at various openings. Checked base idle by blocking IAC hose at air cleaner ( runs slow, nearly dies as it should) TPS switch is in adjustment. Checked valve adjustment: .017-.018 cold. Out of spec but not much.

Details: Worse cold, put in drive and idle is instantly steady
Stop the car warm, let sit for 20 minutes, start and put in drive, Car lurches forward with throbbing idle. Goes away when driving awhile at operating temp,
Although if you watch the tach you can tell it "wants" to act up.
Replace the IAC? 2.3 8V non-turbo auto Rex/Regina

Sorry about the lengthly write up. Starting to get concerned here