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2003 chevy trailblazer_lt
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Discussion Starter #1
All,

I need some input and specifically regarding the intake manifold. I have a 2003 Trailblazer with the 4.2. It's 2 wheel drive.

I've had a bit of an engine idle problem and I did recently buy the car used (less than 8 months ago). It isn't anything major, but sitting at a light the idle rides a little high and even sometimes fumbles on itself like it's about to die (though it never does). I started with the typical things like cleaning TB etc.

I noticed the Intake Manifold seems to have been "adhered" with some glue and appears split down the seam. I don't know if this is some kind of outer shell on the intake manifold or if it goes directly into the intake manifold.

If it is a shell it may not be problematic. If it goes inside the intake manifold then it could easily be sucking air and causing the problems. Does anyone know?

I'm attaching two photos of the small cracks on the sides and the bigger "split" on the seam that has been patched with some kind of pliable adhesive.
 

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2006 saab 9_7x
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Yes, I see them. I think you have to have 5 posts to show pictures and now that you do.........
 

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2006 gmc trailblazer_ls
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That is just the outer shell of the Intake mani. Somebody probably tried to remove the manifold by popping it off. These intakes are pretty difficult to remove but it's just a matter of finding all ten bolts and getting to them. It can be done, it just takes patience.

Now, on to your rough idle ptoblem. There is a very good chance it's your intake manifold gaskets. One way to check if it's leaking is spraying a little bit of starting fluid down around the mating surface of the mani to the head. If it revs up that means there is a leak.

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2003 chevy trailblazer_lt
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Discussion Starter #7
That is just the outer shell of the Intake mani. Somebody probably tried to remove the manifold by popping it off. These intakes are pretty difficult to remove but it's just a matter of finding all ten bolts and getting to them. It can be done, it just takes patience.

Now, on to your rough idle ptoblem. There is a very good chance it's your intake manifold gaskets. One way to check if it's leaking is spraying a little bit of starting fluid down around the mating surface of the mani to the head. If it revs up that means there is a leak.

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I'm guessing to do this on a cold start? Not sure how easily that stuff goes up in flames.
 

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2009 chevy trailblazer_lt
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It's most likely the manifold air pressure sensor (MAP), if the line is kinked or has a small leak, it could cause the engine to idle high or rough due to imprecise readings and overcorrections to A/F Ratios by the ecu.


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Discussion Starter #10 (Edited)
It's most likely the manifold air pressure sensor (MAP), if the line is kinked or has a small leak, it could cause the engine to idle high or rough due to imprecise readings and overcorrections to A/F Ratios by the ecu.


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Okay this leads to a question now... from the comment above, the cracks are simply in the "case" of the intake manifold... yet the MAP Sensor is connected right into the top of that case. When you look at a MAP Sensor it's not a very long tap so I'd be surprised if it's going through the "shell" and into the sealed manifold. (I'm basing this off a video where you can see the sensor looks like it would only barely penetrate the "shell" of the intake manifold...https://www.youtube.com/watch?v=itRXB7MHjX4)

In other words, I'm thinking that in fact it is not a "shell" and that the split plastic is likely creating air leaks which would certainly make the MAP Sensor get all kinds of readings. Pay particular attention to the bottom part of the right image where you can see the "shell" has quite a bit of separation.

Lipka are you certain there is a shell?
 

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2006 gmc trailblazer_ls
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It is indeed just a shell. It is not meant to be removed. If you pull your MAP sensor you will see that it does go through the "shell" and into the intake mani. I have an extra intake manifold from a motor swap I did if you want it. Comes with throttle body and MAP sensor.

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Discussion Starter #12
It is indeed just a shell. It is not meant to be removed. If you pull your MAP sensor you will see that it does go through the "shell" and into the intake mani. I have an extra intake manifold from a motor swap I did if you want it. Comes with throttle body and MAP sensor.

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What's the cost? I see you're up in the North East and I'm down in central texas? Seems most used manifolds around here are $50-$100. I don't know if you could be competitive to meet that.

I'm also considering Rock Auto because they have an aftermarket design that apparently improves on a few things (it's made by Dormann). It's $170 though. Considering this is my daily grind beater I'm likely going cheap.

I still need to spray some starting fluid around though and see if I can find where and if there is a possible leak somewhere. It would be great if it's just a simple MAP sensor and the Shell is of no consequence.
 

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Right I forgot to check where you were. $20 plus shipping and it's yours. I have no use for it. I would recommend cleaning the throttle body and getting new gaskets before installing it.

BUT I still don't think you need it.

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Discussion Starter #14
Right I forgot to check where you were. $20 plus shipping and it's yours. I have no use for it. I would recommend cleaning the throttle body and getting new gaskets before installing it.

BUT I still don't think you need it.

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Does it have the MAP Sensor with it? If so, then i might as well buy it from you since replacing the MAP will cost as much. If not, then let me first run the starter fluid around it to see if find a leak. If not, then I'll replace the MAP sensor and see. If still no good, I'd be happy to buy it off you (assuming shipping to 78759 is reasonably priced).

I appreciate it by the way!
 

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Yes it comes with the sensor . I'll check on shipping.

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Yes it comes with the sensor . I'll check on shipping.

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In your experience would I be seeing a MAP sensor error code being thrown though if it was bad because I don't have that code. Seems like online I should be getting something like a P0106, P0107, or P0108.
 

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If the sensor was bad, yes I think you would be getting a code. Not saying I couldn't be the sensor though. Usually fluctuating idle and stumbling like you said is a vacuum/intake leak. Many times once the engine is warm it won't be as noticeable because the gasket or whatever is leaking will expand with heat and seal it better.

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Did you try cleaning the throttle body? If not, pull it off and spend a little time with simple green and stiff brush and clean it up.

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Discussion Starter #19
Just as a follow up... I fixed a previous issue with a P0440 I've had for a while. It was from the known common issue with the cracked fuel tank filler neck.. I repaired the tank and sealed that. It cleared a lot of other codes I was starting to get related to these surging problems.

Unfortunately the car still has a little surge, but I've also now got the P0420 code for a bad cat so I need to get that code fixed first and will let everyone know if it changes what's currently going on.
 
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