Air Intake Manifold.

[jman_07]

I have a 2002 chevy Suburban 5.3L that when parked overnight in cool weather and started the next morning runs rough idle surges RPM Guage runs normal then sputters and rpms drop for a split second. Constantly has this problem as it does this lights also dim. After the engine is warm and parked for a short period of time it can be restarted and the problem isnt near as bad but still runs a bit rough. Recently had 2 engine codes of P0171 and P0174 truck was taken to a local mechanic he advised me that the air intake Manifold assembly needs to be completely replaced because the plastic material is warped due to age. and that replacing just the gasket wouldnt fix the problem

 

Does this sound correct or could the problem be something more serious because the new plenum is about 800 bucks. Mechanic said this is a common problem with those manifolds.

 

 

 

 

Thanks gueys

 

 

Jared.

[jackyshaikh]

Hi jared

 

Your mechanic said its a intake manifold right? and you are saying plenum.In fact plenum chamber is the top part of intake manifold.Anyway how sure your mechanic is.this dtc's will set when there is vacumn leak this could be from injectors o rings,intake gasket,or PCV valve hoses,or fuel pump.Intake manifold would be rare chance.

[jman_07]

Ok well thats a good start but we defenitly need to find out what the problem is.

 

We got quoted about 1000 bucks for a new intake manifold but this problem is getting worse and the truck runs like absolute crap.

[minibike132]

Hi jared

 

Your mechanic said its a intake manifold right? and you are saying plenum.In fact plenum chamber is the top part of intake manifold.Anyway how sure your mechanic is.this dtc's will set when there is vacumn leak this could be from injectors o rings,intake gasket,or PCV valve hoses,or fuel pump.Intake manifold would be rare chance.

 

With all due respect what are you talking about. There is not a lower intake on this engine the plenum and intake are the same thing. And intake gaskets failing on this motor is almost about as common as having an oil leak on a Harley. The symptoms seem to support an intake gasket. Often times if left unchanged the intake itself will warp. The symptoms of cold start issue going away when warm in no way reflect a fuel pump issue. All of the others are possibilities but usuall will not go away warm. Both a P0171 and 172 would mean both banks and that would all but rule out injector o-rings or individual injector failure.

[jackyshaikh]

I don't know what you mean by saying all due respect.well i agree there is no lower intake on this truck plenum and intake is one unit in your words.In fact we call upper intake as plenum and lower part as intake manifold.may be i'm wrong.

 

In Document ID: 738735 its shown intake manifold as a complete unit,there is no plenum.anyway you said intake gasket failing on this is common yes it is as per document id 1899786 but there is rare chance of intake assembly i said. and due to lean mixture we have found fuel pump problem as well. Even diagnosis chart wont tell you exactly there is only possible causes.hope you won't misunderstood what i typed.

[minibike132]

My problem was that in your original post, it sounded to me, you were telling the OP that an intake is unlikely. Your first post reads to me like you think something else is more likely. I see that was not what you were saying and I appologize. I do however think that rather than tell about the many things that could cause a lean code we should stick to what the OP asked about. You are right needing the intake (or plenum or manifold, whatever we are calling it here) is rarely needed. But I think just about any half competent tech with a can of carb clean and a scanner that can read fuel trim or o2 live can competently diagnose an intake leak. If his mechanic said it was an intake I would tend to believe him unless it was a guess and not a diagnosis. You are right that needing an intake is rare but the gasket is common.

 

Jared, sorry if either of us confused you. The condition you describe added to the codes means there is a lean condition that goes away when warm. A lean condition can be caused by a lot of differnt influences. Low fuel pressure, vacuum leaks and all kinds of skewed sensor readings and fuel control not being calculated by the computer correctly. All that said this engine does have a major problem with the intake gaskets leaking. This is a very common repair. Needing the whole manifold is not that common. The only way to know that you need the manifold and not only the gasket is to take the manifold off and measure it. If your mechanic has not had it apart he can not know that it needs the manifold. This is not to say that he is lying to you or trying to screw you as most people would think in this instance. He has probably been burned by only quoting for the gasket and ended up having to do the entire manifold before. Since he would have to get your authorization to remove the manifold just to know what exact parts were needed you were probably just quoted for both parts. This, in my experience, is less out of a want to take your money and more out of an inability to be able to communicate with the customer about how much labor is necessary to know which parts to quote. In that case shops will quote high and hope it comes out less.

 

I would tend to believe that the problem is caused by the leaking intake if it has been checked out by anyone half way competent. The question is do you need the whole intake or just the gasket. The answer is we cannot tell you without taking it off and making the proper measurements.

[pennzoil29]

jmo, unscrew the oil fill cap, while the truck is running, and if it makes a sucking noise, then you have a serious vacuum leak. I drove my 5.7 for a couple of month's before it ever threw a code. I tried the carb cleaner trick with no luck.

[Wingnut]

Factory intake manifolds for your truck are cheap and available everywhere.

 

Pretty easy to install too.

 

Since they're prone to failure (gaskets)...You could always just pick one up off of Ebay, buy some new gaskets, and knock it out in an afternoon.

[abracadabra]

I know that this could definitely be the intake manifold leaking, since both codes are lean conditions.  But also check the MAF (Mass Air Flow) sensor.  It could be dirty or faulty. K&N air filters can foul up the MAF is the filter gets too much oil. Like someone else mentioned, there could also be a vacuum leak downstream of the MAF sensor.