I found the solution to the problem.
I tried three brand new IACs made by BWD that came from Advanced Auto. I did this because it didn't cost a thing as the first BWD made IAC was installed 6 months ago and came with a one year replacement warranty. I did not have immediate access to a Motocraft part which is why I tried all the BWD parts. What was really crazy was that everytime I tried a new IAC I got different results but the idle RPM was still bad. With one the RPM would oscillate back-n-forth 750-1000 RPM every second. On another the RPM would drop down to 400 RPM then sometimes stall when coming to a stop. Yet another, the RPM would shoot up to 1500+ then drop down to 500 RPM. It just seemed crazy that three new IACs gave different results.
I decided it was time to clean the throttle body (TB). When you take the air intake hose off of the TB there really isn't much to clean. You can clean the opening (left side of pic) to the TB. You can clean the butterfly plate. You can stick your fingers past the butterfly as far as you can and try to clean but really that isn't much of a cleaning. After all, you've barely cleaned into the TB opening at this point. I knew that this little amount of cleaning barely added up to much of anything. In the following picture you see a blue box. The blue box is only there because I was asking what is under the black plate. This is no way is an indication that you need to remove the black plate. I did not remove the black plate and actually do not know what is under the black plate. If someone knows what is under the plate and if removing it can help with cleaning the TB then please chime in.
In the picture you can see the air intake port on the left. Remove the hose clamp and slide the hose off to access the air intake port to clean the inside of it and the butterfly plate. You can see the EGR valve on the right side of the TB.
Before I just buttoned it all back up I took a flashlight and tried my best to look inside of the TB to see if there was anything significant. To my surprise about on the opposite side of the TB air intake opening I saw what looked like a hole had been burned through the aluminum body. It looked like a jagged hole almost like someone took a welding rod and cut into the housing except it looked charred black-brown. After I came to my senses I realized that was a port for the EGR valve (right side of pic) and it was severely clogged (40 - 50%). It was like an ear canal that was closing up due to excessive ear wax.
I took a 7/16" wood dowel and poked the charred area. Sure enough there was a round hole behind that jagged mess. Twisting the 7/16" wood dowel I could barely work it into the hole.
Next, I made a giant Q-tip using a 3/8" wood dowel and part of an old t-shirt I taped the cloth to the wood dowel using electrical tape. I soaked my giant Q-tip with TB cleaner and proceeded to clean out that EGR port hole. Next, I vacuumed out the crumbs. I taped a plastic hose to the end of my vacuum cleaner with electrical tape and sucked all that gunk out. When the cleaning was complete I noted that the 7/16" wood dowel easily moved in and out the hole. This told me that that EGR port is probably 1/2" in diameter. As a reference, the EGR port is about 9" on the opposite side of the air intake port. This is why I needed those long wood dowels to reach it. I don't know if you can take off the EGR valve and clean it from that side. It didn't look like it.
Even though this fixed my problem I am still going to install a Motocraft made IAC valve.
Anyhow, there was my solution. Sure enough the vehicle now correctly idles at 750 RPM. I have read a number of these "rough", "erratic", "high" idle threads. Usually the solution is a new IAC. However, I noted there were numerous folks who continued to have this problem after changing or cleaning their IAC as well as changing out other components. Some even "cleaned" their TB but I really don't think they ever noticed the problem I saw. What was frustrating was that most of these folks never came back with the solution to their problem.
