Hello there! Jose here! I’m new to the forum. I have. 02 ford F-150 xlt 4.6. A few days ago started with some idling problems. RPM too high, at 2,000. I replaced the IAC Valve and the issue gone away. It was working fine until today, just 3 days later after replace the IAC Valve. Any ideas if there is something that cause that IAC valve goes bad or doesn’t work properly. Thanks in advance.

 

Something to consider,
The vehicle's system attempts to keep the fuel going into the cyls within a certain range (14.7 :1 )
Any variation is relayed back to the PCM and adjustments are made accordingly.
When the system gets a message that the mixture is lean, it attempts to correct that by increasing injector pulse width thereby adding fuel to bring the mixture within spec.
I would suspect there may be a vacuum leak allowing UNMEASURED air getting into the cyls and the PCM is attempting to add fuel to compensate thereby raising the RPM.. A thorough check for that addl air getting into the engine might be in order.