I have a whistle that shows up after the truck warms up. I used a small hose as a ghetto stethoscope and found that the noise is coming either from the seam that I am pointing to with the screwdriver or somewhere underneath that piece where I can't reach the hose. (Driver's side of the engine, under the throttle body area)

If I had a vacuum leak here, I would expect a CEL with some lean codes, but it's been whistling for over a week with no codes.

Am I thinking about this correctly?

 

Vacuum leaks will not always throw a cel. Are you sure no one mysteriously stuffed a supercharger in there while you were away from your truck?

 

Haha I don't think so.

I forgot to add that the whistle goes away when I step on the gas, which would point to a vacuum leak, correct?

 

If you think you have a vacuum leak spray some carb clean all around the area and see if the rpms change. If the vacuum leak is very minor the ecu can adjust fuel trim for it. If it has to adjust too much it will set a dtc and the light. And yes.. when you open the throttle vacuum goes down in the intake so vacuum whistle will go away.

 

Cast iron LR exhaust manifolds are notorious for distorting and letting out exhaust. The exhaust manifold on my TD5 started with a slight whistle that got progressively worse and started causing other problems. Although the simplest thing is to throw on a new manifold, it will, in time also distort and cause another similar problem due to heat stress relief in the casting. What my guy did was to have the manifold skimmed and then bolted it back with new gaskets, that way the distortion is eliminated for good. Unfortunately one of the studs broke in the head and required drilling out and a Helicoil insert - but that's another story.

 

let the truck cool, spray the area with clear laqueur paint, and let it dry. The next time to drive your truck if it does not whistle you have a vacuum leak.

 

Mine had a god awful whistle that went away when I had the intake gaskets replaced. It never threw a code.

 

I just did a bunch of work on the truck a few weekends ago, which included replacing the intake gasket. I just wanted to make sure I was heading down the right path before I start working on it again.

 

Yep vaccum leaks are most noticible under idol.

caulk isnt a option, lol