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Old 10-10-2019, 02:50 PM
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Question 4.0 TJ making loud engine whistle

My 03 TJ has had a loud engine whistle for some time now but it only occurs when cold outside most of the time. It wont start until the engine is running for about 5 to 10 mins. It will squeal until i press down on the gas and start again when i let my foot off. It gets progressively louder until eventually it will stop. Ive checked all pulleys and the belt tension, even replaced throttle body gaskets and cleaned the throttle body. Only thing i can think of is a possible air leak somewhere. If anyone else has had this problem it would be a big help to try to fix this. Doesnt effect how the engine performs it is just annoying and can be very loud.

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Old 10-10-2019, 04:27 PM   #2
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Tighten manifold mounting bolts to spec.


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Old 10-16-2019, 10:58 AM   #3
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You may have a big vacuum leak somewhere. Greyhound made a great suggestion with the manifold gasket. It may be sealing itself up when the engine warms.

I had problems with the vent tube that connects between the intake manifold and the rear elbow on the valve cover. There is a short piece of rubber hose making the connection between the end of the tube and the intake manifold. Mine had a big split in the rubber hose.

I tried 1/2 inch heater hose, but it kept splitting. A big vacuum leak would start whistling louder and louder. The engine would not idle down when foot was off the gas pedal, because the computer was thinking it was not getting enough gas (because there was waaay too much air coming into the manifold through the split hose).

I must hav gotten a more flexible bit of hose, because the problem has not returned.
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Old 10-16-2019, 11:01 AM   #4
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Old 10-17-2019, 08:11 AM   #5
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Mine did the SAME thing. Ended up being my manifold bolts were loose. I thought it was a vacuum leak, PS pump, belt, pulleys, etc.. I dropped quite a bit of cash for nothing.
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Old 11-18-2019, 02:37 PM
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I recently tightened all the manifold bolts and even the bolts on the 2 down pipes from the manifold which were a bit loose. Stopped the problem for about 45mins of driving then it resumed the same as before. Might check the hose discussed above but other than that im not sure what it could be
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Old 11-18-2019, 03:31 PM   #7
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My money is on idler pulley. Before you start it on the next cold morning... squirt the backside of the idler with Tri-Flow. If it's the idler your problem will be solved for a couple of days then start whistling again. Pulley is only about $20 if that's what it turns out to be.

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