2.3L ('83-'97) IAC question

[oldgeek]

I took the IAC off to inspect and clean it. I noticed the valve is not all the way shut, there is a small gap. Is it normally shut?

 

[franklin2]

I thought it was spring loaded and is energized to open. I would mark it with a magic marker so you can put it back together correctly, and take it apart a little more to see what you can see.

 

[oldgeek]

I am curious because I can take a screwdriver and nudge the valve up to the seat but it springs right back to where there is a gap. Maybe a 1/32".

 

[franklin2]

Now that you mention that, it's probably how it works. You can tell I am very knowledgeable on this subject

The computer may power the valve closed, and take power off to open it up. The book says the computer cuts the power on and off so fast that it can control the actual position of the valve. That tells me it has a spring in it, I think you figured out it is sprung open.

 

[oldgeek]

Checked the voltage at the IAC valve harness, with the ignition to On and got 12v. Plugged the valve in and the valve did not move, the small gap remains. I'm guessing I need to replace the thing.

 

[oldgeek]

Had an idea. I unplugged the IAC while idling. That had no effect on the idle speed.

 

[RonD]

No, IAC Valve doesn't close all the way when unplugged/unpowered

It only moves 3/8" when fully opened, so not a lot of movement when it is working
But it doesn't take much air increase or decrease to raise or lower RPMs on a running engine

Warm up engine first, 5min or so
Let it idle
Unplug IAC Valve, RPMs should drop to 500-600, barely running or engine may even stall, either is good it means computer using IAC Valve was controlling idle RPMs

If idle doesn't drop it means IAC Valve is stuck or RPMs are higher than computer can control
i.e. idle is 950rpms, computer closes IAC valve all the way but it can't get it lower than 950 usually because of a vacuum leak
With IAC Valve still unplugged and a high idle, start unplugging vacuum lines on the intake and plugging port with finger, see if idle will drop

Warm engine Target idle on a 4cyl engine manual trans is usually about 750-800rpms
Automatic 800-850rpms

On cold start if RPMs are 1,100+ then IAC Valve is working, cold engine needs Choke and higher RPMs, but idle RPMs should slowly drop over the next 5min, to warm engine target idle
Cold target idle is based on outside temp so varies through out the year, the colder the temp the higher the idle
Which is why you want to test on warmed up engine to eliminate the variables

With IAC Valve off and unplugged turn on the key, computer will send 11-12v to IAC Valves wires, you can test that with volt meter
The red wire will have Battery Volts if test to engine ground
The other wire comes from computer and is a variable ground, that's how the voltage is controlled, thru ground side not the 12volt side
Plug volt meter into the 2 wires and see what voltage is, 11-12v

Watch the valve in IAC Valve and plug connector back in, valve should move slightly, if not it may be dead, assuming you had 11-12v on above test

You can move the valve with screwdriver when its unplugged, then try moving it with it plugged in, should be hard to move when plugged in

Motorcraft or Hitachi brand IAC Valves are the only ones that work well on out Rangers, other brands will cause odd issues with idle

 

[oldgeek]

No, IAC Valve doesn't close all the way when unplugged/unpowered

It only moves 3/8" when fully opened, so not a lot of movement when it is working
But it doesn't take much air increase or decrease to raise or lower RPMs on a running engine

Warm up engine first, 5min or so
Let it idle
Unplug IAC Valve, RPMs should drop to 500-600, barely running or engine may even stall, either is good it means computer using IAC Valve was controlling idle RPMs

If idle doesn't drop it means IAC Valve is stuck or RPMs are higher than computer can control
i.e. idle is 950rpms, computer closes IAC valve all the way but it can't get it lower than 950 usually because of a vacuum leak
With IAC Valve still unplugged and a high idle, start unplugging vacuum lines on the intake and plugging port with finger, see if idle will drop

Warm engine Target idle on a 4cyl engine manual trans is usually about 750-800rpms
Automatic 800-850rpms

On cold start if RPMs are 1,100+ then IAC Valve is working, cold engine needs Choke and higher RPMs, but idle RPMs should slowly drop over the next 5min, to warm engine target idle
Cold target idle is based on outside temp so varies through out the year, the colder the temp the higher the idle
Which is why you want to test on warmed up engine to eliminate the variables

With IAC Valve off and unplugged turn on the key, computer will send 11-12v to IAC Valves wires, you can test that with volt meter
The red wire will have Battery Volts if test to engine ground
The other wire comes from computer and is a variable ground, that's how the voltage is controlled, thru ground side not the 12volt side
Plug volt meter into the 2 wires and see what voltage is, 11-12v

Watch the valve in IAC Valve and plug connector back in, valve should move slightly, if not it may be dead, assuming you had 11-12v on above test

You can move the valve with screwdriver when its unplugged, then try moving it with it plugged in, should be hard to move when plugged in

Motorcraft or Hitachi brand IAC Valves are the only ones that work well on out Rangers, other brands will cause odd issues with idle

Thanks Ron for giving me some help here. I need to figure out how to measure RPM's though.

Finding a Motorcraft or Hitachi IAC valve is kind of difficult. Still looking though.

 

[franklin2]

Check for vacuum leaks, and if you have a throttle stop screw on the throttle butterfly, someone may have fiddled with that and opened it too far. If you want to fiddle with it, mark it with a magic marker so you can put it back, and then with the engine warmed up and running, unplug the IAC valve wiring plug again, and then turn the idle stop screw back to slow the idle down. If you turn it back and the engine is still running and the screw is not even touching the throttle, that is a sure sign you have air coming in somewhere else.

 

[-Nate]

Good info here .

Does this mean I can make up a test harness from a junked truck and then use a 12 volt battery to test this IAC valve ? .

TIA,

 

[RonD]

Yes, and no
Hooking up IAC Valve to Ground and 12v will show IAC valve open but it only moves 3/8", you can connect and disconnect 12v or ground wire to make sure its opening and closing, but that's about it

Like many adjustable control solenoid/valves Ford uses PWM(pulse width modulation) to adjust the voltage at the solenoid
And they use the Ground side for this control
Solenoids get 12volts(vehicle voltage) with key on, on one wire
The other wire, the ground, comes from the computer, it is pulsed rapidly(PWM) which changes it's valve's position by raising a lower the voltage at the solenoid

There is another way to do this type of adjustment, called Stepper motors
Stepper motors used voltage pulses to set a position, not the voltage itself
3rd Party are usually combos, stepper/solenoid
So they can work but if a PWM pulse matches a Stepper pulse then position of valve changes, and in the case of IAC Valve engine RPMs can go up and down because of this

 

[-Nate]

Thank you for the detailed response .

 

[scotts90ranger]

Ron, you sure have a way with words and explaining things! I know how it all works but can't get the words to cooperate quite as well...

 

[-Nate]

Well said Scott ;

I'm pretty good on the old stuff but these modern rigs sometimes stymie me .

 

[-Nate]

Hi Ron ;

I did a vacuum leak test and all is well so I'm not looking at new IAC valves, I don't see Hitachi anywhere and zero N.O.S. originals so the next question is, wat other brands are good or known to be less than good ? .

So far I've found :

HERKO # IAC1024

DELPHI # CV10094

Std. Motor products # AC117

Also Walker brand, I didn't catch the P/N though .

Suggestions ? .

TIA,
'