When I first purchased my 2004 TJ earlier last Spring (end of March or so?), soon after having it - in the morning, it would whistle. After a few minutes, it would quiet down and go away - and I wouldn't hear it again, until the next morning.
Researching it led me to believe it was the IAC valve, or possibly the throttle body gasket, or something similar. Let's just say it wasn't any of that, but I got real good at removing and replacing the throttle body (and in the process making my own gasket out of cereal box cardboard for the IAC valve body, because I took that whole thing apart to clean the carbon off completely, without knowing that the gasket was unobtanium)...
The whistle was driving me nuts, so I eventually took it to my mechanic, and let him know my experiences. They only had so much time to check things, because the whistle would eventually go away (within 5 minutes) - then you had to wait for morning again. Eventually they said it was the tensioner and replaced that, and all summer I had no issues.
Then cooler weather (I hesitate to call it "winter" here in AZ - for example, right now it is 63F outside) arrived; in the morning, when it dipped down to the 40s-50s range, cooling the engine off massively - I'd get up to go to work, and the engine would warm up, and once it got to just under the 210 degree mark on my temp gauge, the whistling started again! ARGH!
At first, it was pretty quiet, but as the overnight temperatures dropped, it got louder. Once the engine got fully up to temperature (210-ish) - it would stay whistling, but after 5 minutes or so, it would quiet down. I wouldn't hear it again until the next morning.
While when it first occurred it got on my nerves, plus being embarrassing, when it started whistling this second time, I just cranked the radio and heater fan up some more, and ignored it. I figured I would deal with it eventually. I initially thought "Maybe since it was the tensioner before, it was the idler pulley this time" - not real good logic, but it was impossible to isolate it as to where it was coming from, what with it's loudness, high pitch, my poor hearing, plus all the other engine noise under the hood. I purchased a tensioner with the thought of replacing it at some point.
But before I did so, I did some more checking. I had this feeling that it was temperature related, because of the way it acted in relation to the engine temperature, and overnight temps. I had this thought that (possibly) it might be the fan clutch, or a bearing, or maybe the water pump. Nothing I couldn't fix myself, but none of it I really wanted to touch given the choice - especially if it wasn't that problem. So I did a bit more online digging.
I found that - once I had the right keywords - that this "winter-time whistle" problem was (apparently) common on Jeeps with the 4.0L engine; that it was something many such owners experienced, and that there was a fix for it:
Tighten the exhaust/intake manifold nuts/bolts - particularly the pairs on the extreme ends (toward the front of the engine and toward the firewall):
https://imgur.com/a/XCRyp
So this past Tuesday, when I had a day off (my work "observed" this day for Christmas Eve), I decided to look into making this adjustment. I looked - I still have no clue how you get to the rear pair without removing a whole lotta crap in the way (particularly the fuel rail, injectors, a ton of connectors and wire harnesses), so I figured "Let's try tightening the fronts, I can get to those, and if that doesn't help, then we'll do the rears next weekend".
I first hosed the nuts with some PB blaster and let them sit for a few hours while I worked on other mods I wanted to do (new headlights, mods to my underhood light). After a bit of finagling I managed to get a socket on the top one (with the help of an extension and universal joint), and was able to back it off a bit, then I tightened it back down. I'm not sure of the torque, as I didn't have a torque wrench handy, but I took it as tight as I dared to - no hulking it down - then did the same with the lower (which I had to use a box-end wrench on, due to the angle and other parts like the serpentine belt being in the way). BTW, supposedly all nuts/bolts on the manifold are 9/16" - that's what I used for socket and wrench.
I didn't have much faith that the effort would work, but when I next drove the Jeep on Thursday morning to work (I drove my VehiCROSS in on Wednesday morning), I didn't have a whistle. On Friday morning - though not as early - I didn't have a whistle. I didn't drive it this morning. Tomorrow I should drive it again early, though. Hopefully that was it - a five-minute fix to save some sanity (and $$$).
But again - does anyone know if you can get a wrench on the back pair without needing to take a lot of stuff off (I really don't want to pull the fuel rail, connectors, etc off if I can avoid it - it just seems like a task where you could easily break something important)?
Regardless - I hope maybe this might help or inspire someone out there.
Researching it led me to believe it was the IAC valve, or possibly the throttle body gasket, or something similar. Let's just say it wasn't any of that, but I got real good at removing and replacing the throttle body (and in the process making my own gasket out of cereal box cardboard for the IAC valve body, because I took that whole thing apart to clean the carbon off completely, without knowing that the gasket was unobtanium)...
The whistle was driving me nuts, so I eventually took it to my mechanic, and let him know my experiences. They only had so much time to check things, because the whistle would eventually go away (within 5 minutes) - then you had to wait for morning again. Eventually they said it was the tensioner and replaced that, and all summer I had no issues.
Then cooler weather (I hesitate to call it "winter" here in AZ - for example, right now it is 63F outside) arrived; in the morning, when it dipped down to the 40s-50s range, cooling the engine off massively - I'd get up to go to work, and the engine would warm up, and once it got to just under the 210 degree mark on my temp gauge, the whistling started again! ARGH!
At first, it was pretty quiet, but as the overnight temperatures dropped, it got louder. Once the engine got fully up to temperature (210-ish) - it would stay whistling, but after 5 minutes or so, it would quiet down. I wouldn't hear it again until the next morning.
While when it first occurred it got on my nerves, plus being embarrassing, when it started whistling this second time, I just cranked the radio and heater fan up some more, and ignored it. I figured I would deal with it eventually. I initially thought "Maybe since it was the tensioner before, it was the idler pulley this time" - not real good logic, but it was impossible to isolate it as to where it was coming from, what with it's loudness, high pitch, my poor hearing, plus all the other engine noise under the hood. I purchased a tensioner with the thought of replacing it at some point.
But before I did so, I did some more checking. I had this feeling that it was temperature related, because of the way it acted in relation to the engine temperature, and overnight temps. I had this thought that (possibly) it might be the fan clutch, or a bearing, or maybe the water pump. Nothing I couldn't fix myself, but none of it I really wanted to touch given the choice - especially if it wasn't that problem. So I did a bit more online digging.
I found that - once I had the right keywords - that this "winter-time whistle" problem was (apparently) common on Jeeps with the 4.0L engine; that it was something many such owners experienced, and that there was a fix for it:
Tighten the exhaust/intake manifold nuts/bolts - particularly the pairs on the extreme ends (toward the front of the engine and toward the firewall):
https://imgur.com/a/XCRyp
So this past Tuesday, when I had a day off (my work "observed" this day for Christmas Eve), I decided to look into making this adjustment. I looked - I still have no clue how you get to the rear pair without removing a whole lotta crap in the way (particularly the fuel rail, injectors, a ton of connectors and wire harnesses), so I figured "Let's try tightening the fronts, I can get to those, and if that doesn't help, then we'll do the rears next weekend".
I first hosed the nuts with some PB blaster and let them sit for a few hours while I worked on other mods I wanted to do (new headlights, mods to my underhood light). After a bit of finagling I managed to get a socket on the top one (with the help of an extension and universal joint), and was able to back it off a bit, then I tightened it back down. I'm not sure of the torque, as I didn't have a torque wrench handy, but I took it as tight as I dared to - no hulking it down - then did the same with the lower (which I had to use a box-end wrench on, due to the angle and other parts like the serpentine belt being in the way). BTW, supposedly all nuts/bolts on the manifold are 9/16" - that's what I used for socket and wrench.
I didn't have much faith that the effort would work, but when I next drove the Jeep on Thursday morning to work (I drove my VehiCROSS in on Wednesday morning), I didn't have a whistle. On Friday morning - though not as early - I didn't have a whistle. I didn't drive it this morning. Tomorrow I should drive it again early, though. Hopefully that was it - a five-minute fix to save some sanity (and $$$).
But again - does anyone know if you can get a wrench on the back pair without needing to take a lot of stuff off (I really don't want to pull the fuel rail, connectors, etc off if I can avoid it - it just seems like a task where you could easily break something important)?
Regardless - I hope maybe this might help or inspire someone out there.