Do I Have An Intake Air Leak?

gdoug · April 8, 2007

I have searched all over and My 03 Tahoe 5.3L is experiencing symptoms of an intake air leak. On a cold startup, after the RPM's settle, the engine sounds like it has a cam in it. There is almost a lope to the engine and sometimes it will rock the truck a little. The SES light has not come on though. A few times the engine would drop in RPM to around 400 or so. It seems to be worse when the temperature is colder. It was real bad yesterday after it had been raining and cold.

After the truck is warm it idles almost perfectly. Occasionally, I will see a momentary drop in RPM from the tach and can feel a little roughness in the idle.

Mileage is 103,500

Does anyone have any links that shows how to replace the intake gaskets? I have read it only takes about 2, 2.5hrs to complete the job. I have replaced the fuel injection in my '96 Vortech pickup. It doesn't look like this would be any harder. Does the whole intake come off or just an upper section?

Thanks.

ridnlow · April 9, 2007

Takes about 30 mintues to a hour to pull the intake.. However the newer intakes have O-rings (or the like, cant think of the right word) for each individual cylinder.. Havent really heard of intakes leaking on the gen III engines.. I can take a pic of the bottom of the intake if youd like..

gdoug · April 9, 2007

Here is the TSB I found from another thread:

Subject: Cold Engine Idle Misfire Or DTCs P0171 P0174 - keywords 4.8 5.3 6.0 air cold crack hesitate idle intermittent internal intake leak lean misfire miss P0171 P0174 P0300 power rough surge vacuum

Models: 2002-2005 Cadillac Escalade

1999-2005 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe, Trailblazer

1999-2005 GMC Savana, Sierra, Yukon

2003-2005 Hummer H2

--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

99 through 05 GEN III truck engines may experience any of the following:

A cold rough idle that diminishes as the engine warms up.

Possible DTCS P0171, P0174, or P0300.

Random misfires at idle.

Recommendation/Instructions:

The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.

If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.

The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements.

ridnlow · April 9, 2007

hmm well like i said taking the intake off isnt that hard of a job.. could be done in a hour or so.. good luck on finding the problem.. wonder if you could spray some intake cleaner around the intake to see where it is leaking??

sappy96 · April 9, 2007

How about the throttle position sensor?

gdoug · April 9, 2007

hmm well like i said taking the intake off isnt that hard of a job.. could be done in a hour or so.. good luck on finding the problem.. wonder if you could spray some intake cleaner around the intake to see where it is leaking??

do you have a picture of what it looks like? Do you have to drain the coolant for this kind of job?

Thanks

ridnlow · April 10, 2007

no draining of the coolant.. let me get out in the garage and take some pics..

ridnlow · April 10, 2007

Here is a pic of the seals..

4 Bolts come out of the fuel rail and then 5 or 6 on each side of the intake.. You are going to need a quick disconnect tool to undo the fuel line coming in..

The open holes are of course where the injectors go... you can see where the fuel rail bolts up too.. there is also a couple of hoses you have to undo.. make sure when you reseat the injectors to lube the o-ring with diletic grease..

This pic shows where the coolant runs through the throttle body.. might have a little bit come out.. those hoses are a booger to get off.. while youve got it apart would be a good time to get the fittings and do the throttle body bypass...

cbxeric · April 10, 2007

Do not remove the injector rails. They come off with the intake just fine, just disconnect the two fuel lines and the electrical plugs off the injectors.

gdoug · April 10, 2007

I appreciate all the info. I have started by trying to spray some brake cleaner (only thing I had available)around the intake area trying to see if it made a difference in the way the engine ran. I couldn't really tell anything definite. The leak could be on the underside of the intake as the TSB suggests making it hard to diagnose.

Also the engine ran smoother than normal for some reason when I tried it yesterday. It seems to only be a problem when the temperature falls below 45-50 degrees F. I am wondering if something else is going on that may not be an intake leak.

I just bought this Tahoe about 2 months ago and I am not sure the last time the fuel filter, plugs, etc has been changed out. It has 103K miles and I am sure the injectors could use a cleaning.

How would I get into the TB to clean it? Mine is a 2003 and it uses a motor to open and close the throttle plate. There is no cable attached to the throttle. I don't want to damage something.

ridnlow You mentioned something about a throttle body bypass. What is that exactly?

Thanks again!

ridnlow · April 10, 2007

If you take take the intake tube off you could just spray the seafoam or whatever on the bottom of the blade and then through the little hole in the TB..

The throttle body bypass is where you hook the two hoses that run coolant through the throttle body together, thus bypassing it.. its pretty much a free mod.. you can really feel it on a cold day..

BRZ71 · April 10, 2007

I had the same problem and changing the gaskets fixed mine. Was an easy fix. Although I am not a big fan of Autozone I got my gaskets from them for 35 for the set, GM dealer wanted 85. Well see if they hold up, but they were felpro gaskets so they should.