Possible intake gasket leak

[Blaze69]

I've got a 2002 tahoe with the 5.3 flex in it. Recently I started to get some very weird things happening to it. It may be cause it's starting to get colder in the mornings or maybe just chance. It hesitates and seems like it wants to die. After it warms up or when it is actually in gear and running it is fine.
I tried spraying some cleaner around the intake to see if the idle would change (nope). I have read somewhere that GM made a mistake and put in the wrong colored gasket (orange instead of green I think) for the flex fuel engines.
Is there some other test to try to narrow it down? Or does anyone have any ideas as to what else it could possibly be? One other school of thought says it could be the temp switch is not reading correctly.
Thanks

[dailydragger03]

In my experience a temp sender will usually throw a code if its acting up. How many miles? Have you ever changed plugs and wires? My 03 was surging a little bit at idle. I changed plugs and wires at 86k and it went away.

[67ChevyRedneck]

This may sound crazy, but clean and tighten the battery cables.

[Blaze69]

I'm sitting right around 61000 miles. I've changed the plugs from stock to the bosch plats and back to stock over the last few years. I've yet to change the wires, although I have been contemplating it.
Now, I understand how a loose battery cable could cause problems with the computer not getting the correct amount of power, but how would it be causing problems only when it's cold. I will try that out when I get home in the morning.

[truckdude239]

i would go more for a temp senser seening that when it is cold th computer riches the fuel to help it warm up faster. by the way these trucks come with plat plugs from the factory that are suppose to be good for 100k miles. i had one at work the other day that had 156k on it i replaced the plugs and they looked fine, only changed because of the miles on them

[Blaze69]

I thought that the PCM when into a open mode (but still monitors all the sensors) when the engine was cold and then once it reached a certain temp it would go into the closed mode and actually start controlling and making adjustments. One other thing about this is where is the actual sensor located? I read somewhere that it was on the drivers side near the radiator.
What about the IAC motor? Could it have an effect on this? Does the computer use this in a open mode?

As for the plugs, there was no reason for me to change them originally, I just did to try something new (the bosch platinum 4). I ended up going back to the original because I really saw no improvement. Isn't the factory plug an Iridium based plug?

[dailydragger03]

Yes the plugs are iridium and rated for about 100k (AC 41985 for both flex and gas). Its pouring rain right now so I can't look at my truck to verify this, but I think the temp sensor is in the driver's side cylinder head. Its possible there are 2 of them, one for the gauge and one for the ECM. If the rain lets up I'll try to take a look and get a picture for you. As for the IAC, I'm not sure.

[Blaze69]

Located on the head, never would have guessed. I guess that's why boards like this are a wealth of info. If you could get a pic that would be great. Thanks.

[dailydragger03]

Well no luck with the pic because my engine driven compressor for my suspension blocks everything on the driver's side of the motor. I was out in town this morning so I stopped by work and looked it up on mitchell. There are 6 different engine vin's, which is the eighth digit. If the engine vin is a W its on the rear of driver's cylinder head, T U or V its on the front of the driver's cylinder head, a 1 is on the front of the intake manifold in the center, a G is on the center of the right cylinder head. Here are a couple of part numbers incase you need them NAPA# ECH TS5732 or you can by delphi parts at napa now DELPHI# DEM TS10076. Hope this helps.

[dailydragger03]

any updates?

[Blaze69]

Hey Daily,

Thanks for the info, but I've got one small problem with it. My engine code is a "Z". I didn't see it located in your list. Any thoughts on that?

Thanks

[dailydragger03]

Well from what I can find the T and Z vin codes have the same location which is the front of the driver's cylinder head.

[truckdude239]

this should be it my shop key says t and z are the same

[Blaze69]

Great, looks like it is in the same place as the one for an older 350. My 69 blazer had it right about there. Is this the one for the gauge or ECM? Or are they one n the same. I'll go ahead and buy one in the morning and then try and throw it in on Monday or so.
One last thought on it though. For future reference, look back up a few posts where I was wondering about the closed/open mode. Does anyone know exactly how that works and how it may affect my situation? Hopefully if all goes well I will post up by midday on Monday, or probably Tuesday morn to check it while it's cold. Thanks for the info.

[dailydragger03]

I did a little research today while I was at work and it seems there is just the one sensor. At least that is all that is listed in napa's system and paper catalogs. I'm not sure about the open/closed loop stuff.

[Blaze69]

Update:
Well, I replaced the temp sensor today and fired her up. I really can't say if it worked or not. The weather here isn't as cold as it was last week. I guess what I should have done was try a before and after to get a more accurate result. I suppose I will have to hope for colder weather (they say it's supposed to rain here in the valley on turkey day).
I have thought about this alot and I don't think I really understand it. What effect does the coolant temp have on the way my engine was/is running. I would figure that there should be an external temp sensor that would tell the ECM what the ambient temp is. Any thoughts???

[Blaze69]

Okay, here's the latest. Since I've replaced that sensor the engine hasn't acted up like it was. It is starting to get colder here (at least down to the low 50's so far). I can't say why it did what it did, but if it is the fix then yahoooo!

Thanks.

[Blaze69]

Latest update:
The sensor did not fix the problem. Now that it's gotten colder here the problem is back in full force. Did some reading on it (again) and here's what I came up with. Tried to locate some vac leaks with a sprayer filled with soapy water. On Mon is was raining and cold. Started it up and within a minute or so it was stumbling. Started spraying all around the intake. While I was under the hood I noticed that when I sprayed the passenger side between #4-6 the exhaust cloud grew. Let it go back down to normal and sprayed again, sure enough. It's an intake leak. So, I'll have to order up the "new" correct gasket and get it put in sometime here in the next week or two.
Funny how spraying it with tb cleaner before yielded a negative result. Just some info to pass on for someone else to use.
Oh yeah, I did try to tighten up the bolts with no luck.

[Blaze69]

Well the chore is finally complete. I took it apart last week and it took me about 4 hours from start to finish. Both the intake and the heads were dirty, dirty. Tested it over the last week and it runs just fine now. Hopefully it'll be good for another long spell. And, hopefully it brings my gas usage down a bit. lol

[truckdude239]

did you flush teh coolant system and use a green mixure? if ya did it means no more problems

[Blaze69]

Coolant flush? I changed to green about 10-12k ago.

How would the coolant give this sort of problem anyway? The coolant doesn't go up that high does it? I could be missing something though...

[bwood]

Intake gasket/coolant leaks were issues on the Gen I engines. The intake leaks on the Gen III engines (4.8, 5.3, 6.0) were just air leaks (coolant doesn't flow through the intake on the Gen III)

[LEEVON]

x2 here. Did the wife's 2002 Tahoe 5.3L flex fuel two weeks ago. Hard starting, knocking in the extreme cold, and throwing codes P0174 and P0171. It wouldn't stumble with carb cleaner so I took a chance and replaced the intake gaskets with GM's teal replacements at $120 (OUCH). Runs like a champ. Mama's happy again.