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Unread 01-30-2016, 08:44 AM   #1
tecumsa
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Vacuum leak ?

I think i resolved an idle problem I've been having, but the last thing the mechanic suggested I look into was a vacuum leak. I checked it using the smoke method and found no leaks, but I have a question before I call this resolved. The problem rears its head after the engine comes up to normal temps, is there a part of the vacuum system that only engages then? When I did the testing I did it without warming the temp up fully. I didn't think that would really matter, but thought I would ask.

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Unread 01-30-2016, 08:55 AM   #2
cilantropena
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I am having similar issue with 87 yj. Starts and runs fine. When warms up stalls during deceleration. Previous owner did some work inder the hood. Wondering if vacuum lines right. Also hear bubbling noise from
Air cleaner housing. Could it be pulse air check valves or cat? 4.2 6cyl 2bbl carter
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Unread 01-30-2016, 05:24 PM   #3
mukluk
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Quote:
Originally Posted by tecumsa View Post
I think i resolved an idle problem I've been having, but the last thing the mechanic suggested I look into was a vacuum leak. I checked it using the smoke method and found no leaks, but I have a question before I call this resolved. The problem rears its head after the engine comes up to normal temps, is there a part of the vacuum system that only engages then? When I did the testing I did it without warming the temp up fully. I didn't think that would really matter, but thought I would ask.
What problem, specifically, are you experiencing?

There aren't any components in the vacuum setup per se of a TJ that operate based on temperature. It is possible however, for a crack to exist in part of your engine's intake system or for a part of the same to be loose, and when either of which heat up and expand they may then allow a vacuum leak to develop.
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Unread 01-30-2016, 05:28 PM   #4
mukluk
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Quote:
Originally Posted by cilantropena View Post
I am having similar issue with 87 yj. Starts and runs fine. When warms up stalls during deceleration. Previous owner did some work inder the hood. Wondering if vacuum lines right. Also hear bubbling noise from
Air cleaner housing. Could it be pulse air check valves or cat? 4.2 6cyl 2bbl carter
You may have better luck getting an answer in the YJ or CJ sections of the forum: CJ Forum link, YJ Forum link
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Unread 01-31-2016, 08:46 PM   #5
tecumsa
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Quote:
Originally Posted by cilantropena View Post
I am having similar issue with 87 yj. Starts and runs fine. When warms up stalls during deceleration. Previous owner did some work inder the hood. Wondering if vacuum lines right. Also hear bubbling noise from
Air cleaner housing. Could it be pulse air check valves or cat? 4.2 6cyl 2bbl carter
I don't remember the '87, I don't think it had an air temp sensor, I would guess you might have a problem with the auto choke. Back then I had a Jeep truck and always had problems with the auto choke, got so bad that I eventually replaced it with a manual choke.
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Unread 02-01-2016, 03:19 PM   #6
tecumsa
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Quote:
Originally Posted by mukluk View Post
What problem, specifically, are you experiencing?

There aren't any components in the vacuum setup per se of a TJ that operate based on temperature. It is possible however, for a crack to exist in part of your engine's intake system or for a part of the same to be loose, and when either of which heat up and expand they may then allow a vacuum leak to develop.
Okay, that is what I was asking. Thanks

What I was experiencing (posted it here several times over the last few years) is a drop in RPM when dropping into neutral to coast down a hill, towards a stop sign, or in stop-and-go traffic. The problem only occurs in the winter months when temps drop into the 30's and below. Turned out to be a faulty (not bad) IAT/MAT sensor. I think there is still a problem because it's not 100% resolved, but that could be because of a cheap sensor from AdvanceAuto. I had to return one already because it was totally bad, and AA refused to replace the unit (pissed about that).
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