Possible Vacuum Leak (manifold gasket failure)

Nwteig

Nwteig

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Coming up on 8 months ago, I found that my revs were starting to increase at idle, from 750 to 1000, to now idling around 12-14 hundred. For a while, I let it be because it had no effect on power, now I am starting to notice my drop in efficiency and clutch wear. I believe the high idle to be a vacuum leak. I also believe I found one in the intake manifold as when I spray carb cleaner near the gasket on the back part, it starts to increase RPM (see videos). Could this leak be the cause of such a high idle? Please let me know what you guys think.
 

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I am not sure what the issue is, but my rpms shoot up when I turn my Jeep on sometimes. I also have an issue when I shift from drive back to park. My rpms shoot up and stay high for a few seconds and then come back down. I thought maybe it was a sticky throttle, but it still does it after cleaning it.
 
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SirDoopYJ said:
I am not sure what the issue is, but my rpms shoot up when I turn my Jeep on sometimes. I also have an issue when I shift from drive back to park. My rpms shoot up and stay high for a few seconds and then come back down. I thought maybe it was a sticky throttle, but it still does it after cleaning it.
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How high? I think mine idles at around 16-1700 briefly when cold and then it comes down. It’s normal; but if you’re going much higher than that then maybe something to look into.
 
machoheadgames said:
How high? I think mine idles at around 16-1700 briefly when cold and then it comes down. It’s normal; but if you’re going much higher than that then maybe something to look into.
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I believe that is where it shoots up to, no more than 2,000. I just find it weird it does it about every time I shift from Drive to Park.

Automatic Problematic Lifestyle :cool:
 
SirDoopYJ said:
I am not sure what the issue is, but my rpms shoot up when I turn my Jeep on sometimes. I also have an issue when I shift from drive back to park. My rpms shoot up and stay high for a few seconds and then come back down. I thought maybe it was a sticky throttle, but it still does it after cleaning it.
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This is a 5 speed and a warm engine. The revs stay that high for the entirety of the engine operation.
 
SirDoopYJ said:
I believe that is where it shoots up to, no more than 2,000. I just find it weird it does it about every time I shift from Drive to Park.

Automatic Problematic Lifestyle :cool:
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Ah, if it’s doing that every time you go to park then you probably do have something causing a high idle.
 
Nwteig said:
My engine never goes below 1000 rpms.
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Sorry I never addressed your actual post, but yes the intake manifold can cause sky high rpm if it's bad enough. Based on your videos you need to change that gasket. To put it in perspective, sometimes people change their exhaust manifold and don't get their intake seated properly in the process. They start the Jeep up after and they go way up to redline. Make sure your intake manifold is seated on the dowels and torqued properly and you should be good. And I mean that after getting a new gasket installed.
 
Speaking of manifold gaskets, my '92 YJ 2.L had a factory gasket which only covered the intake manifold and the exhaust was steel against steel with the cast iron header against the head.

The rebuild kit had a full length gasket which covered both intake and exhaust ports. My concern was that using the full gasket would cause the exhaust header to sit slightly further from the head (width of the gasket) and now the two flanges for intake and exhaust would not be even and may not be secured properly by the one bolt that covers both flanges.

As it turned out the thick gasket compressed enough where it hasn't been an issue.

Intake Left / Exhaust Right

1635950067737.png
 
Flyer58 said:
Speaking of manifold gaskets, my '92 YJ 2.L had a factory gasket which only covered the intake manifold and the exhaust was steel against steel with the cast iron header against the head.

The rebuild kit had a full length gasket which covered both intake and exhaust ports. My concern was that using the full gasket would cause the exhaust header to sit slightly further from the head (width of the gasket) and now the two flanges for intake and exhaust would not be even and may not be secured properly by the one bolt that covers both flanges.

As it turned out the thick gasket compressed enough where it hasn't been an issue.

Intake Left / Exhaust Right

View attachment 118755
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Can you send me a link for a rebuild? We’re you having similar symptoms?
 
Nwteig said:
Can you send me a link for a rebuild? We’re you having similar symptoms?
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I had a different issue when the oil pressure sending unit broke open and dumped all the oil on the road. The engine was trashed when I bought it. I bought a master rebuild kit and had a local machine shop redo the cylinders and crankshaft. I did all the assembly.

No link for the rebuild but I followed the Factory Service Manual which you can find in this forum. Very detailed instructions which will help.

Link: https://wrangleryjforum.com/forums/yj-resources.121/
 
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