Replaced iac still revving up to 2000 rpm, then will go sometimes but then hard to

Hello, It's likely nothing to do with the idle air control valve. It's likely to do with the engine's processor compensating for data seen from either a mass air leak or an intake leak or a vacuum leak.There are several possible causes related to atmospheric pressure, fuel trims and related components. Too hard to know without hands on testing. www.repairpal.com/repair-shops