Whistle sound at specific throttle position

01 Cherokee Sport.

4.0 L6, stock.

When I bought my XJ a year ago, I noticed a quiet whistling sound at about 1/3 throttle, the sound isn't audible at any other throttle position. I thought nothing of it at that time, but now it's getting louder and annoying, I also have a CEL, but that's been on since I got the truck.

My educated guess is that an injector seal is bad, but usually, it's a loud whistle at IDLE, which is not the case here. The CEL is on due to an Evap issue (surprise surprise am I right?) and I'm wondering if the intake pressure sensor is tripping due to a bad injector seal.

It's pretty self-explanatory, I've just been working to fix the little issues and this one is next on the list, and I would post it here to see if anyone else had this issue and fixed it somehow.

Fix the problem(s) causing the CEL trouble codes. See if the whistle clears up. If the whistle sound persists, I would file a radius on the Idle Air slot inside the throttle body. That worked for me.

Get a 3' long section of 1/2" hose, stick one end in your ear and wave the other end around listening.

Most of the time its a throttle body leak, usually the main gasket gets brittle and cracks. Sometimes its the sub-housing for the IAC. Can also be wear around the butterfly seals.

Ditto ehall's suggest to use a hose to probe for the source of the sound. Alternatively,
I use a medical stethoscope with the diaphragm removed (open hose end). ~ $15.

I've had this whistle, twice, on 2 separate XJs. On both cases it was the intake/exhaust
gasket. The OEM gasket is a sandwich of fiberboard and a sheet metal core. Sometimes
the fiberboard developes a leak and the metal core acts like the reed on a saxophone.

I would use a stethoscope, but the engine needs to be under load for it to happen, therefore I need to be going down the road. The PO replaced the intake/exhaust gasket about a year before I bought it, I am not sure about the throttle body gasket though, my guess is that he probably didn't so I will probably get one and throw it in to see what happens, that's a project for this weekend.

You say stock and I acknowledge that, but I have to ask: does it have any kind of aftermarket intake on it? Those K&N style intakes will do that. It's very pronounced at that same throttle position too.

Agreen said:

You say stock and I acknowledge that, but I have to ask: does it have any kind of aftermarket intake on it? Those K&N style intakes will do that. It's very pronounced at that same throttle position too.

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nope, stock intake

Well my '88 did this twice. One was an intake manifold leak after I changed my exhaust manifold. Had to redo it. ugh!

The other was my TB gasket. A little high temp silicone took care of that.

Mine whistled on deceleration. No noise at steady throttle or acceleration, but as soon as I let off, thar she blows! However, I heard mine in park/neutral as well as while driving.

man, I'm really hoping it's not the intake/exhaust gasket haha. I think I am going to make a temporary cereal box gasket to put on the TB just to see what happens, I've got high temp silicone that I can use but I like to use it wisely.

fjxj0103 said:

<snip>I think I am going to make a temporary cereal box gasket to put on the TB just to see what happens</snip>

Click to expand...

lol, haven't heard that in a while.

That’s me for ya, lol, I got too many boxes lying around here


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Thinking about this again. You might try to fiddle with the HVAC vent controls to listen
if the whistle pitch changes. The hard plastic vacuum lines at the HVAC vent control
are know to develope a hairline crack, and whistle.

Good point, but last year I replaced my heater core, and Noticed one of the lines was completely broke (probably from me yanking on the assembly trying to get it out) and I ended up replacing all the lines in there before putting it back in.