So....my 2002 F150 XLT 4.6 V8 2WD had recently popped the Code For IDLE AIR CONTROL VALVE (p1504).

I have been trying everything and can't get idle back to normal.

Bought new IAC...which didn't work. Also...if you take IAC truck but leave plugged in, should the plunger move when you turn key to On position? My new one didn't.

After changing, I drove 30 miles and let cool down and went to do it again with the A/C on and lights to try to help...but it didn't.
Checked all vacuum lines and pcv valve...no luck. Have taken all lines off and checked for cracked and wear and have even added some electrical tape to the seams in case.
If I give the truck gas when starting, I can eventually get it to idle below 500 for some time, but when I go to unplug the IAC, nothing changes at all.
I even unplugged the throttle position next to it at one point and that didn't change anything either.


I recently just fixed a p1704 code dealing with exhuast....but don't know if that matters.

So.....is there anything else that can be causing this problem that you can think of? It worries me because its only the same 1504 code that keeps coming up over and over.

Is there any way that the computer isn't sending the correct voltage? Could it be shorted somewhere?

Any help would be greatly appreciated. Thanks

 

the problem can only be a bad iac, pcm or wiring
you have ruled out the iac...it should ohm out at 6 to 13 ohms


the red wire should have full battery voltage
the white. light blue wire is grd by the pcm. check for short to power, disconnect the pcm and iac conneotor and ohn check it, then chek for short to grd. if its all ok you need a pcm

 

The problem ended up being the wiring harness. When I probed the IAC and the harness with voltmeter I was getting the correct numbers. Apparently this was because the probe was getting a better connection than the actual harness was....but didn't know that.

Out of frustration and 3 IAC valves, I decided to start messing with the harness and eventually got revs from the engine showing that the connection was bad.

To save time, I just cut the harness off and soldered the wires to the IAC valve and that is all I needed to do.

Easy fix but super annoying to find it.

 

I am experiencing this very same issue. I have done many of the same steps you have.
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 when discussing code reading ?

so While I wait for all your replies, I removed the IAC solenoid and applied 12 volts temporarily to the terminals of it, ( on and off again and repeat type of action) 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? My meter readings from testing at the harness connector for the IAC are 11.6 volts.

Because of your post, Tomorrow i will clean the wire harness of mine with contact cleaner and reconnect to the IAC and hope this helps mine. I'll let you know my results. If you have further suggestions and tips I would welcome hearing them.

 

Its really good to hear about your resolving !!