Idle / low throttle whistle noise on 4.0

[vito2772]

Hi all,

Jeep has been running great recently, but all of a sudden today when I drove it I could hear an audible whistle coming from the engine bay. No check engine light, Idle is normal and when I give an gas I don't hear it any more(above 2krpm). I had the hood up trying to listen where it is coming from. It isn't coming from the throttle body, if i lean my head over the left side of the engine bay, it sounds as if it is coming from the AC unit area, the left side middle of the engine bay.

It happens whether the AC is on or off and doesn't change. How could I track this down? Could it there be a hairline crack in the exhaust manifold? Should I do a smoke test?

I was thinking if I remove the belt that will tell me whether it is the engine itself or an accessory component, but I haven't done that yet.

Just want some input.

 

[TJ_owns_a_TJ]

Having same issue - I ended up replacing the throttle body gasket and giving it a good clean with carb cleaner - also replaced the idle air control sensor while I was at it, because why not. Still get the whistling - it is most likely a vacuum leak somewhere and while not super urgent should eventually be addressed, next step is to smoke test it and see exactly where it's coming from. Following this thread to see if anyone has different input on it.

 

[LJBean]

That type of whistle can be caused by a vacuum leak at a gasket. Two common areas are the throttle body, as TJ_owns_a_TJ mentioned, and intake manifold. I had a similar whistle when lifting up on the throttle and solved it by finding an intake manifold bolt that had backed out a bit.

 

[jrmcafee]

Seems like this same issue emerged for me last night. Thought it might have just been a change in the weather (much cooler in TN this week now) and it wasn’t warmed up enough but it persisted this morning after well beyond 210. Had a chance to get under the hood and listen and it really doesn’t sound like it’s coming from the intake manifold/TB side.

I ran my hand over the hoses from the airbox and crankcase breather to see if I could feel any vacuum being lost but nothing there. I think it is probably a gasket leak or cracked hose but got a video to see if any of you think differently about it.

So as I’m thinking through it, could be the weather indirectly. Especially if it’s a hose. Hot weather here in TN might cause some material expansion in a hose just enough to mask it until it cools off this time of year.

 

[macleanflood]

Spray some carb cleaner around and see if the engine blips.

-Mac

 

[AndyG]

The “L” s at the intake manifold on the drivers side are prone to crack from exhaust heat.

 

[thepassivelapse]

I'm having the same whistle but only at idle and when below freezing. I've found that the heater doesn't blow hot since this has started. I think it's somthing with the ac but it's hard to run a vapor test in -18.

 

[macleanflood]

I'm having the same whistle but only at idle and when below freezing. I've found that the heater doesn't blow hot since this has started. I think it's somthing with the ac but it's hard to run a vapor test in -18.

What's your temp gauge showing? Have a scan tool or a Bluetooth ODB reader and Torque Lite or Pro? PCM should show the coolant temperature.

Just struggled through changing out my thermostat.

-Mac

 

[Rickyd]

I'm having the same whistle but only at idle and when below freezing. I've found that the heater doesn't blow hot since this has started. I think it's somthing with the ac but it's hard to run a vapor test in -18.

Vacuum line going to the hvac from the intake is intact? It goes to a bottle under the battery and then through the firewall by the heater core