IAC question

2trux · Jan 28, 2015

Because of idle problems I removed and inspected the IAC.

What I observed:
When the solenoid is removed valve closes and stops airflow.
Valve rod moves smoothly and spring returns it to closed.
When solenoid is on, rod is pushed and air can flow.
When installed on engine, air is always flowing through IAC. Even at high RPM.

Does this sound like the IAC is not working correctly? Should air stop going through the IAC at high RPM? Should the valve be completely closed with key off?

Thanks

wizkid00104 · Jan 28, 2015

I didn't observe mine moving, but I cleaned it with carb cleaner and it changed how my truck idled. That is how I knew the valve needed replaced. I believe the seals in mine wore out.

cvar · Jan 28, 2015

Read this: http://www.explorerforum.com/forums/showthread.php?t=84220

2trux · Jan 29, 2015

@cvar I read that link and I have cleaned mine twice. I think the solenoid has gone bad.

Last night I blocked off the IAC and used the idle screw to set the idle. This got rid of the fluctuating idle speed. Because of this I do not think it is working correctly, so I have ordered a new IAC.

RonD · Jan 29, 2015

Fuel injected engines all use IAC(or AIS) Valves to set idle, no jets to meter fuel, so there is no "idle screw".
There is a screw on the throttle linkage, it is there for a couple of reasons.
To adjust TPS's(throttle position sensor) minimum voltage, .7-.9v on Fords
Anti-diesel and anti-stall, with IAC Valve closed(unplugged) you can use it to set minimum air flow above stall, so 500-600rpms.

Minimum RPM MUST be below Computer's Target warm engine RPM or IAC Valve can't control minimum RPM
Manual trans Target is 650-700
Automatic 750-800
So you need to be below these when IAC valve is closed all the way.

Check TPS minimum voltage after adjusting this screw, .7 to .9v throttle closed, measured from center wire on TPS connector with key on engine off, open throttle all the way and you should see above 4.5v
TPS often has slotted bolt holes allowing small adjustments to set these parameters.
If you are checking TPS voltage also check if throttle cable has stretched, open throttle manually and remember voltage, say it is 4.8v, then face meter towards cab and use gas pedal to open throttle all the way, if you get 4.4v cable has stretched.
Google: ranger throttle cable mod

TPS like IAC Valve are learned parameters, they have preset ranges like .7-.9 minimum and above 4.5 for Wide Open Throttle in the case of the TPS but computer needs to learn actual voltages.
So when you adjust or replace anything on a computer controlled engine, unhook negative battery terminal for at least 5 minutes, or reboot computer with reader/scanner.
When re-powered the computer will start to relearn

2trux · Jan 30, 2015

RonD said:
Fuel injected engines all use IAC(or AIS) Valves to set idle, no jets to meter fuel, so there is no "idle screw".
There is a screw on the throttle linkage, it is there for a couple of reasons.
To adjust TPS's(throttle position sensor) minimum voltage, .7-.9v on Fords
Anti-diesel and anti-stall, with IAC Valve closed(unplugged) you can use it to set minimum air flow above stall, so 500-600rpms.

RonD, agreed the screw does not meter any fuel, but by opening the throttle it will do what the IAC does by letting air in to the engine. It is not dynamic as the IAC is but I was using it to see how the engine ran with the IAC blocked off. The IAC on my engine never seems to close, even at 2500 RPM there is still bunches of air being sucked past the throttle through the IAC.

Before the engine was pulled out there were times that the engine would idle at 2000-2500 RPM. This past performance and what it is doing now is what led me to order a new IAC.

RonD said:
Check TPS minimum voltage after adjusting this screw, .7 to .9v throttle closed, measured from center wire on TPS connector with key on engine off, open throttle all the way and you should see above 4.5v
TPS often has slotted bolt holes allowing small adjustments to set these parameters.
If you are checking TPS voltage also check if throttle cable has stretched, open throttle manually and remember voltage, say it is 4.8v, then face meter towards cab and use gas pedal to open throttle all the way, if you get 4.4v cable has stretched.
Google: ranger throttle cable mod

Thanks for the info on the TPS minimum voltage, I will check this. I replaced the TPS right after I bought the truck because it had no voltage output.

IAC question

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