I was under the impression that there is a hole in front of the throttle plate that lets air into IAC and computer decides how much goes out to the engine. But after seeing how much carbon was on intake port (assuming intake ofcourse) It can't be all fresh air from air filter side. Upon googling, I see there is a pcv input also. So how many air inputs are to this IAC lol connecting to the input hole at IAC? Also the aftermarket IAC don't have a spring anymore. Does the heavy-duty spring keep the IAC in open or closed position until ecm presses against it to shut off or open IAC air supply?

 

Year, model, and engine, please?

 

1999 expedition 4.6 2v

 

Keep in mind that the IAC is simply a computer-controlled bypass valve around the throttle plate. Inlet air will come from anything upstream (towards the air filter). You'll have to just take a look at your intake tract to identify everything.

 

Wondering what the source of black carbon on the valve and the port is if it is coming from fresh inlet air towards the air filter?

 

Inspect the plumbing. Any hoses or inlets upstream of the IAC?

It's been way too many years since I've owned a V8 of that generation for me to remember.

 

Deleted. I was wrong and don't know how to delete the reply.