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Old 12-19-2011, 06:59 PM   #1
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high idle after manifold replacement

yes, i have searched.

yes, i know threads like this exist.

changed my exhaust mani today, and the install went smooth. just over 6 hours working alone pretty much.

anyways, i have an extremely high idle. 2500-3000. i found no leaks, triple checked all vac connections, and i even sprayed some carb cleaner around the mani just to make sure it wasn't sucking in air.

i want to cry. please help?

is my mani REALLY leaking? did i not install it right? the guide pins lined up beautifully, and i am really stumped..


any and all input is very much appreciated.

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Old 12-19-2011, 07:02 PM   #2
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Those high rpms are caused by nothing more than a vacuum leak. There is a 99.9999999% chance the vacuum leak is coming from where the intake manifold was not properly positioned over the head's locating studs which will prevent an air-tight seal. Even though it looks properly positioned, I'm still betting it's not. The same thing happened with another poster here who also claimed his intake manifold was properly positioned. It turns out his intake manifold was not correctly positioned after all.

Make sure your other vacuum lines, especially the larger one between the intake manifold and power brake booster, are all properly connected.

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Old 12-19-2011, 07:24 PM   #3
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....are you saying i have to do this whole thing.... again???


hahahahahahahahhaah wahhhhhhhhhhhhhhhhhh
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Old 12-19-2011, 07:28 PM   #4
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Sorry, I hope you don't so check you vacuum hoses first... maybe you'll get lucky and discover you forgot to reconnect one, like the big vacuum hose that connects the power brake booster to the intake manifold.
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Old 12-19-2011, 07:28 PM   #5
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i am 100% positive all vac lines are in their respective places. i guess i am left with no other option but to remove the manifold, and reinstall it. the only problem i have is how will i know that it is correct the second time around?
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Old 12-19-2011, 07:32 PM   #6
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...the only problem i have is how will i know that it is correct the second time around?
No guarantee but I'd bet big $$$ you'll be a lot more careful getting it seated correctly the second time around which will probably do the trick. Any vacuum leak at all provides air to the engine in exactly the same way like if you were holding the throttle body valve open.
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Old 12-19-2011, 07:33 PM   #7
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No guarantee but I'd bet big $$$ you'll be a lot more careful getting it seated correctly the second time around which will probably do the trick. Any vacuum leak at all provides air to the engine in exactly the same way like if you were holding the throttle body valve open.
will you come to CO and do it for me????





at least i dont have to remove the header. that part sucked major ass.
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Old 12-19-2011, 07:53 PM   #8
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All I can say is that you're in very good company, someone posts that they're having this same problem here at least once a week. I think the last one happened on Sunday, maybe Saturday. It's common, too bad it had to happen to you.
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Old 12-20-2011, 12:17 AM   #9
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All I can say is that you're in very good company, someone posts that they're having this same problem here at least once a week. I think the last one happened on Sunday, maybe Saturday. It's common, too bad it had to happen to you.
hopefully some of those will see the thread, chime in with some info..

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Old 12-20-2011, 09:00 AM   #10
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did you disconnect the battery to reset the PCM?? I doubt that will clear it up, but it is worth a shot.

So, if you spray carb or t-body cleaner around the manifold, the idle does not change??? Do you have a map gas torch?? You can crack the valve on one of them, and move it around the manifold and vac lines to see if you have a leak, the idle will change.
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Old 12-20-2011, 10:53 AM   #11
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did you disconnect the battery to reset the PCM?? I doubt that will clear it up, but it is worth a shot.

So, if you spray carb or t-body cleaner around the manifold, the idle does not change??? Do you have a map gas torch?? You can crack the valve on one of them, and move it around the manifold and vac lines to see if you have a leak, the idle will change.

Yes I tried that.. I have tried carb spray without much luck unless I am doing it wrong... I have Map gas, but I don't understand the process you mentioned
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Old 12-20-2011, 04:47 PM   #12
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Your rpm's were fine before you removed the intake manifold. They are now high after reinstalling it. Stop worrying about tests to confirm it is leaking from where it is bolted to the head, which it is, get out of analysis paralysis and just reseat it.
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Old 12-20-2011, 06:46 PM   #13
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Your rpm's were fine before you removed the intake manifold. They are now high after reinstalling it. Stop worrying about tests to confirm it is leaking from where it is bolted to the head, which it is, get out of analysis paralysis and just reseat it.
i will!!! tomorrow!
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Old 12-20-2011, 10:43 PM   #14
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the only problem i have is how will i know that it is correct the second time around?
When you fire it up and the high idle is gone.
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Old 12-21-2011, 12:07 AM   #15
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When you fire it up and the high idle is gone.
should i drink my 40 before, during, or after??????
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Old 12-21-2011, 01:41 PM   #16
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fixed!!!! thank you all!!!!!!!!!!!!!!!!!
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Old 12-21-2011, 05:13 PM   #17
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What was it?
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Old 12-21-2011, 08:07 PM   #18
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What was it?
If it was anything other than the manifold not seated correctly, he would have been unable to resist saying so. Since he didn't do that, we both know what the problem was.
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Old 12-22-2011, 09:09 AM   #19
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when you're right, you're right!!!!

thank you ALL!
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Old 12-22-2011, 01:36 PM   #20
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Sometimes you suspect it's leaking, but you don't want to just assume it is - if you are wrong it's too much work for nothing.

A simply way to verify - connect a vacuum hose to the manifold vacuum port. Blow cigarette smoke in the hose - if the manifold isn't seated properly you'll see the smoke come out where it shouldn't.

Use a strong pencil beam flashlight to help see it. You may have to stuff a rag in the TB to help hold the smoke in.

A 2 minute test.
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Old 12-22-2011, 09:13 PM   #21
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here are the two cracks in my manifold:
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Old 01-07-2012, 03:13 PM   #22
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Sorry to revive this older thread, but I just did mine today and my rpm's max out when i start my Jeep up. All hoses connected. The only 100% way to know if the intake manifold is seated right is to start it up?
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Old 01-07-2012, 05:16 PM   #23
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Maxed rpms is a clear indication your intake manifold is simply not properly seated against the head. Just read the above posts.

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