My 1989 Econoline 150 van has the 5.0L in it and it has developed a very high RPM at idol.
I removed and cleaned the idol air control valve. It is working freely and no carbon build up now.
I checked the idol air control valve to be in spec or not... it is in spec..
I removed the EGR position sensor and checked it to be in spec or not, it is in spec.
EGR freely moves up and down.
So I still have this very high idol issue...like 3000 RPM idol!
What do I check now that could be the source of the problem?

I was just outside looking for vacuum leaks. Found none.
Engine starts right away. every time.
If i disconnect the wiring harness from the solenoid of the idol air control, the engine dies immediately.
and I am following the school of thought that.... once you disconnect the IAC, the idle immediately drops to the minimum idle speed set by the"non- adjustable screw adjustment." Once you plug the IAC back in, the idle typically jumps back up to the idle speed the computer wants to idle it at. .... is this correct?

So what would cause the solenoid on the idol air control valve to fully open the by pass air valve and hold it open? ,
and not allow it to close down some in order to slow the idol of the engine? but instead, keep it fully open??
I discovered that, Opening the egr valve manually does nothing to slow the engine rpm.
I discovered that having removed the egr position sensor and manually depressing and releasing and again depressing the plunger on the egr sensor, has no effect on engine RPM. ...wondering if this is normal?
..as i was under the theory of thought that adding exhaust gas to the intake mixture would lower the rpm some?

So, when I disconnect the wiring harness from the solenoid of the idol air control, and the engine dies immediately, .... I have the impression that the solenoid is working. But could it be fully "on" and not operating as a variable movement solenoid, like I think it is designed to be?
if I am correct, then, what would cause the solenoid on the idol air control valve to fully open the by pass air valve and hold it open?

What do the letters: KAM stand for with regards to resetting something?

While I wait for all your replies, I'll share that I removed the IAC solenoid and applied 12 volts temporarily to the terminals of it, ( on and off again and repeat) expecting to see the plunger inside move. I saw no movement, i heard no clicking. if the solenoid is good, I'm thinking i should have seen back and forth movement of the plunger, am i correct to think this?..would no movement indicate a bad plunger...even though earlier test with the VOM indicated the solenoid to be with in specs?