P1506 code high idle

[Dc4704]

I have the V6 SOHC engine and I recently replaced the lower intake manifold gaskets and IAC valve which solved the issue of stalling on startup. However, now my car is throwing a P1506 code. It idles from 1700 to 2000 at all temperatures and when i unplug the IAC it drops to 1500. This is with the idle set screw all the way out. I tried checking for leaks but I found none. Any ideas?

 

[2000StreetRod]

sticking throttle plate?

P1506 Idle Air Control Over Speed Error

This error means that the PCM recognizes the idle speed is excessive but is not able to reduce it using the IAC valve. Air is entering the intake manifold somewhere. Some members have had problems with the IAC valve to intake manifold sealing properly. There's a very thin figure 8 gasket between the two. The absence of lean codes indicates that the excess air being intaked is going thru the MAF sensor. That reduces the possibility of an intake leak including the IAC valve gasket. Another possibility is that the throttle plate is not closing properly. It could be sticking or there may not be any slack in the cable. Also check the TPS: Ford Explorer - Ranger TPS Test Procedure

 

[Dc4704]

After driving around with my high idle all this time I decided to tackle diagnosing it again. I found that a spark plug was really loose. Torqued it back down and idle improved significantly! Cleared the code and hoping it doesn't come back. Just in time for inspection too

 

[Steeda04SVT]

Just started to get this same code and put in a new IAC from Oreilly's and still have the same code. But I hear a "hum" from the engine area by the factory air box and when I unplug the IAC the "hum" stops until I plug it back in. I felt around but didn't hear any air hissing just the hum from the air box area. Any ideas?