I have a 2000 Saturn sedan 1.9 8v sedan with a 5 speed manual transmission. I have always had a high idle problem but recently put another engine in the car (same Vin code). Upon starting it the engine idled extremely low but once warm it revs up to 1600 rims and down up a down. I have recently changed the evap purge solenoid, IAC, ECT, TPS,
Intake gasket, and cleaned the throttle body and intake thoroughly. The revving still persists. Could ecm be the issue? Any help would be nice. The only code it shown now is high voltage iac. Thanks.

 

Have you checked for a vacuum leak?