Cold start up Whistle coming from drivers side engine V6 2007 Sport.

[Drcoffee]

I have noticed with the deep cold snap we had in the midwest area, that when my truck fires up it sounds normal with the typical roar. Then as the idle settles at a high rpm, its still okay. But as the idle drops to about 1000 rpm, I hear a high pitched whistle down to about 900rpm. Then as rpm drops further, it goes away.
The sound comes from the drivers side above the exhaust up on the intake somewhere. I sprayed carb cleaner just about everywhere on the side of the intake and hoses with no change in rpm or sound. I saw where v8 guys were having the same issue but no real solution. Has anyone here found and solved this problem on their truck? Its an 07 sport with 230,000 miles. I assume running high rpms with the throttle body closed on cold gaskets is allowing some air to get in, but from where. Do these plastic intakes crack? Should I just start replacing vacuum hoses?

 

[ktom3001]

Alternator?

 

[Drcoffee]

Its only whistling for a few seconds, 5-10 seconds at the most. So narrowing it down is a challenge. I did listen by the alternator but its coming from higher up.

 

[Ph03n1x24]

Its only whistling for a few seconds, 5-10 seconds at the most. So narrowing it down is a challenge. I did listen by the alternator but its coming from higher up.

Maybe you installed a supercharger and just forgot. hehe
The fact that it comes and goes tells me it's likely coming from the pulley system i.e. a bearing starting to go. A slight misalignment of the serpentine belt could also chirp or whine when it's cold. The alternator could be suspect as well. I've gone through a couple on my 4th gen. With your head under the hood any sporadic engine noise can sound omnidirectional which can make it difficult to pinpoint. Also, some solid state components can make a squealing noise under mechanical stress, although unlikely the source of your problem.

 

[Drcoffee]

I know what you mean. This is definitely a vacuum whistle. And it just could be a design flaw in the plastic intake runners which is only a problem with super cold air. I cant say for certain because the windows are closed, but I thought I heard it while driving at highway speed.

Just an aside, I monitor my LTFTs and I see 7-9% (lean and adding fuel) on both banks while cruising and near 0% at idle. Thats why I am troubleshooting this whistling.

 

[Ph03n1x24]

I know what you mean. This is definitely a vacuum whistle. And it just could be a design flaw in the plastic intake runners which is only a problem with super cold air. I cant say for certain because the windows are closed, but I thought I heard it while driving at highway speed.

Just an aside, I monitor my LTFTs and I see 7-9% (lean and adding fuel) on both banks while cruising and near 0% at idle. That's why I am troubleshooting this whistling.

Did you check for a possible crack in the upper air intake manifold you mentioned? Plenum intake gaskets could also be bad. Is there a throttle body spacer? (Troubleshooting I found on an older thread on another forum)

This might help narrow things down:
ABN Mechanics Stethoscope
Amazon.com: ABN Mechanics Stethoscope – 2 Piece Automotive Stethoscope Kit Car Stethoscope Automotive Engine Diagnostic Tool : Automotive

 

[Drcoffee]

I changed the fuel injectors a year ago. I replaced all the intake and TB (no spacer) gaskets at that time. I didnt think to physically inspect the plenum but should have.

 

[waypoint]

Just an aside, I monitor my LTFTs and I see 7-9% (lean and adding fuel) on both banks while cruising and near 0% at idle. Thats why I am troubleshooting this whistling.

LTFTs are a good troubleshooting info source, especially where unmetered air is suspected. 0% idle seems to rule this out, though.

If you can get access to a smoke machine that's a good next step.

 

[waypoint]

I changed the fuel injectors a year ago. I replaced all the intake and TB (no spacer) gaskets at that time. I didnt think to physically inspect the plenum but should have.

Might want to whip out your torque wrench and hit the plenum and TB bolts again to verify they're still tight.

This might account for the noise only present on cold temp starts...as the engine warms up and components expand to close the leak.