Po508 Dodge Dakota trouble code

Did you replace the actual IAC or just the air flow sensor? If just the sensor then you replaced the wrong part, run the full diagnostic procedure for the IAC and if it indicates a bad ISC unit then remove the old unit, clean ports with throttle body cleaner, install the new ISC, clear the codes and then do the drive time protocol. That means start it and drive it like you normally would for 20 minutes without shutting the engine off. If the check engine light comes on during that time then something else is not right and the protocol will end, you will have to fix the code and start all over again.