Still trouble shooting code p.o. 172 ...if I unplug the connector to the valve, hot engine rpm stays about 900 rpm....removed valve, looking inside shouldn't the valve be closed it's slightly open about 5mm...oh crap i should have turned engine off and unplugged then start engine.....ide about 600.so it looks ok ...could not delate this message lol

 

9.8 ohms across terminals IAC is off engine

 

You can test IAC Valve after it has been removed
Plug its wires back in and turn on the key
Valve should open all the way, computer does this for starting the engine
Unplug the wires and valve should close all the way

Repeat plugging in the wires and unplugging them as much as you want to make sure valve is not sticking.

IAC valve gets 12volts on the red wire with key on
Other wire goes to the computer, computer Pulses the Ground to open and close the valve.
Key on = full ground, so valve is open all the way
Unplugging 12v and ground lets it close all the way, spring pushes it closed

 

Ron. With IAC off the valve is open a few mm, key on nothing it does not move ... it has 12 v at red wire... but starting cold engine the mornings the rpm starts around 1500rpm then drops to 900 as it warms up, so does the engine have to be running so the computer can control the openings.. bench testing the IAC valve its not closed, with 12v the valve opens a few mm but does not close all the way, could this be my problem lean bank 1.... i also noticed when the A/C compressor kicks in the rpms dont increase

 

Computer grounds IAC valve at Key ON, so it will open fully for starting

So measure voltage on the two wires with key on, should be battery voltage, 12.x
If lower then computer is pulsing the ground and shouldn't be

All fuel injected engines REV at startup, that because IAC Valve is fully open, but RPMs should drop instantly as computer lowers voltage by pulsing ground

It is possible the computer software in your year also looks at ECT sensor(coolant temp) to see if engine is warm, and doesn't open IAC fully if so.


I would pick up another IAC from wrecking yard and see how it opens and closes
Ford used same IAC Valves on many different engines

 

Yes I agree .
I can get a walker IAC Valve from Amazon $32.50 plus tax

 

Got the new part today, seems to work better, rpm comes down quicker at cold starts, hot idle around 800... the new IAC Valve was slightly open like the old one..before fitting