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Discussion Starter · #1 ·
Have an 04 Envoy with the 5.3L, I have 92k miles. . I bought the vehicle in Feb of 08. In March, once I got over the excitement of having heated seats and a new ride,:excited:, I started noticing a slight skip in the engine. It was really noticeable if I was just sitting still in park with the engine running. Took it back to the dealer, they said it was within specs, got it back and decided it must just be the nature of the vehicle. Well while working one day, I repo'd a TB with the 5.3, and it didnt have the skip. Decided to do the simple things before taking it back to the dealer and paying the deductible for the warranty work. After all that, same thing, took it into the dealer, they found that my fuel pump was only placing 46psi when it needed to be presenting in the 60s-70s.(I think those are the numbers). They said, that would fix it. It helped with gas mileage, (still getting 14.6avg), but not the skip. Below is a list of things that either I or the dealer have replaced or done(in order).

new plugs, new wires, air filter, fuel filter, Seafoam(Direct through brake booster), new plugs, new wires, fuel pump.

I am running out of things to do. any suggestions. possible intake manifold leak? tb needing cleaned? coil pack?:undecided
 

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2005 chevy trailblazer_ls_ext
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Clean the Throttle Body. It's really easy to do.
:iagree:
Also - if that doesn't work, before you throw any more parts at it, you need to do or have a compression test done.

Something you could try first is to use some Techron in the gas tank, and maybe a top tier gasoline (Like Shell, Chevron, etc.)
 

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Erratic idle that goes below 600 RPM on the tach without setting the Check Engine Light is usually the dirty throttle body. If you ever get a CEL light, you can read the codes and it should even tell you which cylinder has the intermittent spark.

And if anybody ever said they changed spark plug wires for you, you should slap them for lying. We have no spark plug wires in the usual sense because the coil packs sit on the plugs. I was wrong here. OOOOOps. Was used to dealing with I6 engines for so long I forgot about the V8.
 

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Rough Idle!

I have an 04 TB I have cleaned the throttle body...Added Seafoam in thru the brake vac booster....changed the fuel filter....changed the plugs....STILL have the rough idle....HELP!
 

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And if anybody ever said they changed spark plug wires for you, you should slap them for lying. We have no spark plug wires in the usual sense because the coil packs sit on the plugs.
do the V8's also have coil on plug?
 

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2002 gmc envoy_slt
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What about the PCM, has it ever been updated? - I know the I6 PCM for '04 had a glitch in it, was there a similar issue for the 5.3, which GM released a patch for?

If there was a intermittent mis-fire, the PCM should through a code after a while of constantly seeing the mis-fire. That leads me believe it is most likely not a misfire issue with the plugs, wires or coils, although a coil would be the most obvious. Problem is that you don't really know which coil, although we may be able to narrow down the problem to a specific cylinder.

If you have access to a non-contact temperature sensor, I'd read the temps on each of the cylinder exhaust ports and verify they're all within a couple of degrees of each other......the 'cool' cylinder is the culprit.

Another way is to connect an inductive timing light to each plug wire, one at a time and see which one flashes the light in harmony with the burp or skip.
 

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Misfire code on cylinder

After cleaning the throttle body...fuel injectors...new plugs....seafoam...fuel filter...map sensor...then reading codes it showed a misfire on cylinder number 5....so i switched the coil pack with cylinder number 4 and reread the code and it showed number 4 misfiring so i ordered a new coil pack....will no tomorrow if it solves my rough idle and rough acceleration. if not then i will have a compresion test.....or do you think i should have a pcm update?

thanks to all of you and this forum its been the best!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 

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After cleaning the throttle body...fuel injectors...new plugs....seafoam...fuel filter...map sensor...then reading codes it showed a misfire on cylinder number 5....so i switched the coil pack with cylinder number 4 and reread the code and it showed number 4 misfiring so i ordered a new coil pack....will no tomorrow if it solves my rough idle and rough acceleration. if not then i will have a compresion test.....or do you think i should have a pcm update?

thanks to all of you and this forum its been the best!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That should fix it for ya man!


As for the OP, any updates? Most of my experience is with the I6 but Im curious if you've found an answer as I want to make sure my SS doesnt do this...
 

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Hey there where no updates! Just the Flash needed for the 4x4 switch!

My TB is running like new! the last item needed after all other goodies done was one coil pack!
 

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Discussion Starter · #14 ·
havent had time to do any work on the voy. Did get bored and took the TB off the other day. it surprisingly was not very dirty. However, I did find quite a bit of oil coming out of the valve cover vent tube, that then is placed right back through the throttle body. I believe that is what it is. If I was told correctly by my ls2 guy, this is may be part of the emissions. But I should not be have that much blow by. I am assuming a bad pcv, but instead of spending any more money in guessing and testing, I have 300 miles left on my warranty(extended). Called the GM dealership, told them about the oil, and they said, yea, not normal. I have an appointment monday. Once I get a diagnostic, I will post with the anwser. Its been nice having a warranty and not having to work on it, but in another 300miles, I will not have that option. eh, oh well, just time to build the engine up.:D:crazy:
 

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Discussion Starter · #16 ·
see, I have no idea. This is my first GM vehicle. I have only had Ford products before, I know I know, shhhh. There is a hose that comes from the valve cover up to a port on the left side of the intake manifold. That port, then continues through to the front side of the TB. It appears to be a vacuum line, but with my knowledge only in ford 4.6's and 5.0's, I have no idea(I feel dumb).Its hard for me to explain, but its too late to pop photos.

There is also an un-normal amount of water coming out of the exhaust.
 

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Discussion Starter · #17 ·
Update: Just got off the phone with the dealership. It has an intake manifold leak. I will keep you posted on whether or not this fixes the skip. In the meantime, back to driving the rental Hummer around. hehe.
 

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Discussion Starter · #18 ·
The skip is 90% fixed. It still has a slight skip, but according to the dealership, this is caused by the spark plugs. I have a set of Autolite Platinums in it. Before that I had Bosch Platinum's. Dealership said it has to have Iridium plugs in it. Since it was in for warranty work, unless I wanted to pay the arm and the leg to have the plugs and wires replaced, I will have to do them myself. No biggie. Now I must recover from the rental car costs, and I will throw Iridium plugs and new wires back in. ughhh.
 

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The skip is 90% fixed. It still has a slight skip, but according to the dealership, this is caused by the spark plugs. I have a set of Autolite Platinums in it. Before that I had Bosch Platinum's. Dealership said it has to have Iridium plugs in it. Since it was in for warranty work, unless I wanted to pay the arm and the leg to have the plugs and wires replaced, I will have to do them myself. No biggie. Now I must recover from the rental car costs, and I will throw Iridium plugs and new wires back in. ughhh.
Oops double post. See below
 

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The skip is 90% fixed. It still has a slight skip, but according to the dealership, this is caused by the spark plugs. I have a set of Autolite Platinums in it. Before that I had Bosch Platinum's. Dealership said it has to have Iridium plugs in it. Since it was in for warranty work, unless I wanted to pay the arm and the leg to have the plugs and wires replaced, I will have to do them myself. No biggie. Now I must recover from the rental car costs, and I will throw Iridium plugs and new wires back in. ughhh.
I would ask the dealership if they know what spark plug was in there from the factory?

I can tell you - in my 05 there were A/C Delco Platinums. Part number 41 - 981
Of course I have the I6, but I suppose the V8 COULD be different but I doubt it. Maybe someone else with the V8 will chime in.
 
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