Not a Ranger related problem, but I need help

[MorganMcCann]

I'm helping my buddy replace his lower and upper intake manifold gaskets on his 2000 v6, and we got everything put back together. The engine runs, except there is a loud honking/humming / bad noise that comes out of the intake. That noise goes away if you unplug the IAC. We put a new IAC on the mustang. The same thing happened with the new IAC. What could this be?

When the IAC is unplugged it runs like a champ, much better than before.

 

[RonD]

You have a vacuum leak, I know stating the obvious

Warmed up engine should idle at 500rpms or stall with IAC Valve unplugged, either is fine.
For it to "run better" with IAC unplugged it means you have a vacuum leak.

Leave IAC unplugged and with engine idling, make sure all the vacuum lines got hooked back up, at BOTH ends.
Spray some carb cleaner or starting fluid around lower intake gasket, if RPM changes you found a leak, same for upper intake gasket.

Make sure PCV Valve "rattles" so clean, also Vent hose(valve cover to air intake)

Also unhook the battery at some point for at least 5 minutes, that will reboot the computer so it will relearn IAC settings.

 

[MorganMcCann]

It will idle at 500 with the IAC unplugged. It just makes noise like crazy with it plugged in.

 

[Spott]

When the IAC is unplugged, at idle, the engine should lug way down or stall. Is this engine in stock configuration, or have there been performance adjustments or modifications?

Running well with the IAC unplugged indicates a vacuum leak, or a stuck IAC (it's unlikely that both IACs are stuck open, so look for a vacuum leak.) Vacuum leaks can occur with bad hoses, disconnected hoses, or gasket problems.

I can't think of any reasonable cause for the IAC to be humming, unless you hooked the wrong wires up to the IAC. That should be difficult, as Ford should have used unique connectors for different parts, and the wires would be different lengths. Double check the wiring anyways. Maybe some wire insulation has failed and two wires shorted together while you were moving the harnesses around.

 

[MorganMcCann]

I'll tell him that. This 2000 Mustang has been so much more of a pain than my 98 v6 was to replace the intake manifolds.

 

[MorganMcCann]

Could some other sensor be telling the IAC to do that? Like a tps sensor?

 

[MorganMcCann]

https://www.youtube.com/watch?v=yXx5bS4lxVM

This isn't the mustang, but this is the noise it makes.

 

[RonD]

Remove air cleaner lid and/or air cleaner, start engine.

Unplug MAF sensor, engine should stay running, CEL will come on.

Unhook intake air plenum and pull it off the intake and out of the way.

................................==IAC Valve==
Air filter/MAF=====//..throttle plate..\\====Intake/engine

IAC Valve works like above, there is an air passage on the air filter side of the throttle plate, this passage by-passes the throttle plate, the IAC Valve controls the air being let thru this passage.
With passage exposed, and noise happening put you finger on the throttle plate, see if it is vibrating and making the noise.
The IAC air passage will have ALOT of suction on it, you can try your finger but I would suggest having a glove on, lol, or use a rag to block air flow thru IAC Valve.
The IAC valve can vibrate and make that noise, even new ones.
If the noise goes away with passage blocked then it is the IAC valve making the noise.

When unplugged IAC valve closes all the way so it can't vibrate.

 

[MorganMcCann]

The IAC was reversed. That fixed it.

 

[RonD]

?? never seen that or even heard of that.

Glad it is fixed

 

[MorganMcCann]

It was a super simple mistake, and a super simple fix. I like those the best.