IAC Test Question?

[Alan_nc]

94 Ranger, 3.0, Auto, AC

So I've done the IAC checks with the engine running. I was watching a video of how to check an IAC (on a Toyota) and he applied voltage to it on the bench to check if it would open and close.

Sooooo….can I do this on my IAC? And if I can do this: What voltage and to what terminals?

 

[RonD]

IAC valve is just a solenoid with a spring so has no polarity
It is a 12volt device

Inside is a coil of wire around a metal cylinder, it becomes an electro-magnet, same as a relay works, when 12v and ground are applied, in either direction, so no polarity
But it also has a spring, like a relay, that holds the valve closed

The IAC Valve gets 12v on its Red wire with key on
The computer Pulses the ground on the other wire to regulate voltage at the IAC Valve, so 5v to 12v is used to adjust how much the valve opens

With no voltage applied you should be able to move the valve a bit with a small screw driver
With voltage applied it should be hard to move the valve

There should be NO connection to the case of the IAC Valve from either electrical terminal on the valve, i.e. metal case is NOT a ground on this device, the two connections are isolated from the metal case

 

[cbxer55]

IAC valve is just a solenoid with a spring so has no polarity
It is a 12volt device

Inside is a coil of wire around a metal cylinder, it becomes an electro-magnet, same as a relay works, when 12v and ground are applied, in either direction, so no polarity
But it also has a spring, like a relay, that holds the valve closed

The IAC Valve gets 12v on its Red wire with key on
The computer Pulses the ground on the other wire to regulate voltage at the IAC Valve, so 5v to 12v is used to adjust how much the valve opens

With no voltage applied you should be able to move the valve a bit with a small screw driver
With voltage applied it should be hard to move the valve

There should be NO connection to the case of the IAC Valve from either electrical terminal on the valve, i.e. metal case is NOT a ground on this device, the two connections are isolated from the metal case

Cool information. For some odd reason ,I always thought there was an old style electric can motor in there fluctuating the valve. Learn something new every day.

IAC related question. I have an old school MAC CAI. When the truck is cold, and driven cold, there is a loud whistle that escapes the intake. It goes away once warm. I mean loud, head-turning loud. Shrill. Is that the IAC working it's little heart out trying to keep the air intake correct while cold? Once warmed up, it just has an evil hiss while idling. And a roar that overcomes the mufflerless exhaust at full honk.

 

[RonD]

You are thinking of a type of Stepper motor or step motor, which many car makers used for this type of valve

This is often why 3rd party IAC Valves don't always work well in Fords, they are 2 wire stepper type


There is a Vent on an IAC valve, has a plastic cap on it, this is BEHIND the internal valve so not a vacuum leak, or shouldn't be
It allows the valve shaft to move in and out without building up air pressure behind it, so an equalizer vent
If the internal seal starts to leak then it can make a "whistling" noise because intake vacuum is sucking in air

There is also a vacuum operated "air pre-heater" on the Rangers stock Cold Air Intake
When engine is cold a vacuum operated vent switches the intake air, for air filter housing, from in front of the grill to pull air from around the exhaust manifold until engine warms up a bit
This helps engine warm up and also lowers emissions during warm up

If these vacuum lines are unplugged or cracked then you could get a "whistling" sound during warm up

 

[cbxer55]

I don't believe my 98 had that whatyamacallit that took air off the exhaust manifold when cold. Didn't see anything like that and no extra open vacuum lines. I don't think it's a vacuum leak at the IAC because it only does it when cold. Plus my IAC is a Hitachi. I appreciate the info. The whistle doesn't bother me at all, I was just curious as to why it happens. I would say my Lightning does it, it has the exact same IAC. But the blower makes so much noise with that cog drive, nothing else can be heard over it. Starts whining as soon as it's running.

I recall when I first put the CAI on the Ranger 18 years ago, it still had the stock Ford IAC. And it whistled exactly the same as it does now with the Hitachi. About the time the temperature needle crosses over the C on the gauge, it stops.

The one and only vehicle I've ever owned with a tube from the exhaust manifold to the airbox was my 78 Trans Am (threw it all in the round open top file soon after buying it). Haven't seen a contraption like that in years. I thought that was just for carbureted vehicles.

 

[RonD]

All vehicles have the air pre-heater, its an emissions thing, but its often removed, or not reinstalled after engine work

There should be 2 vacuum lines on the air cleaner housing, thats the pre-heater control, one will go to intake the other to the vents vacuum "motor", should be under and in front of air filter box

 

[cbxer55]

All vehicles have the air pre-heater, its an emissions thing, but its often removed, or not reinstalled after engine work

There should be 2 vacuum lines on the air cleaner housing, thats the pre-heater control, one will go to intake the other to the vents vacuum "motor", should be under and in front of air filter box

Well, I threw the stock airbox in the trash years ago. I reinstalled it once to see if I could tell a difference between the CAI and stock. Oh yeah, big time. Got rid of it so I'd never be tempted to try it again. But I don't recall there being any vacuum lines attached to it. I am quite aware the things that can happen leaving vacuum lines open, so if they were there, I'd have plugged them. I'll go give it a looksee today. I don't have any lean codes showing at this time, so far as I know there are no vacuum leaks present.

 

[Alan_nc]

I'm at 17-20 on vacuum and have been chasing any minor leak. What it the down side of plugging the vacuum lines to the air box?

 

[RonD]

No downside except slower warm up, assuming air pre-heater system is intact

 

[cbxer55]

Maybe mine never had it, or it was deleted before I bought it. I bought it in January 2000 with 10,000 miles on it. I looked for vacuum lines today, NOTHING! Not a one. I removed the stock airbox when I put the MAC CAI on it in 2002. I couldn't find squat today when I looked for them.