2008 GMC Sierra Denali - Rough Idle on Start

[FourthandShort]

I had a quick question about an issue that started recently and hasn't gone away.  

 

When I start my truck after having it sit over night, it will idle rough and in some cases, I get warning lights that the Stabilitrack and Traction Control Systems need service.  I get the CEL on, and after a few moments, everything settles down and it runs fine.  

 

I was concerned it was a bad tank of gas, so I ran the tank through and filled up a few times and now the problem seems to have lessened but is still happening every so often.  I hooked up my computer and its not throwing any codes.  However on one cylinder, I saw a history of a few misfires.  Not a lot, but some.  

 

Any ideas?

[sefiroxx]

Idle problems can set a Bunch of random codes so fix the idle problems first.

You'll need to identify the specific cylinder so get a better scanner or loaner. Could be plug, wire, coil, injector, harness.

[FourthandShort]

11 minutes ago, sefiroxx said:

Idle problems can set a Bunch of random codes so fix the idle problems first.

You'll need to identify the specific cylinder so get a better scanner or loaner. Could be plug, wire, coil, injector, harness.

Thank you for the feedback.  The scanner is telling me its cylinder number 4 with the misfires.  Should I just change them all?  

 

Also the scanner isn't pulling an codes, it tells me no codes found.  The lights come on and then after a few seconds, everything clears up. 

[sidemouse]

The problem is cars today, people put gas in the tank, change the oil on occasion and maybe throw an air filter at it every once in a blue moon and then 100k miles later wonder why it doesn't run like it did new... Unfortunately without some kind of a maintenance records history the possible causes for a rough idle are almost endless...

 

So I am going to guess ...

7mm OEM spark plug wires that have been on there since possibly when that thing rolled off the assembly line, probably the spark plugs too.

Usually misfire at idle and hard to start means gap gone wide due to erosion, among other things...

Replace spark plugs, gap .030- .035 and

Replace spark plug wires, I would recommend using 8mm ones.

 

That's if you can't remember when they were last done, or if they were done more than 4 years / 50k miles ago.

Start there, then we move on to other things.

[diyer2]

Well if the OP has to ask if he should change them all that's a sign IMO.

No maintenance until theres a problem would be my guess. 

 

[sefiroxx]

Thank you for the feedback.  The scanner is telling me its cylinder number 4 with the misfires.  Should I just change them all?  
 
Also the scanner isn't pulling an codes, it tells me no codes found.  The lights come on and then after a few seconds, everything clears up. 

If you are running the original plugs, you might as well change all of them. Check cyl 4 plug for carbon build up - an injector may be stuck open. Use a timing light to see if it is firing. If not swap the coils with another cyl to see if the misfire moves. If yes, a new coil is needed, if not, a new wire is needed

[Bankrupter]

IMO id start with a - full- tune up if its not had one since you've owned it  Plugs, wires, filters (including fuel filter). If there is a problem after that. I'd compression test all 8. I could give you 10 reasons right now that would only waste money if the truck has had poor maintenance to this point and the basic troubleshooting has not been done. You can swap the cylinders ignition with another and see if the problem moves. But again if not in top maintenance just do the work. 

[FourthandShort]

 

On 6/1/2019 at 12:57 AM, sidemouse said:

The problem is cars today, people put gas in the tank, change the oil on occasion and maybe throw an air filter at it every once in a blue moon and then 100k miles later wonder why it doesn't run like it did new... Unfortunately without some kind of a maintenance records history the possible causes for a rough idle are almost endless...

 

So I am going to guess ...

7mm OEM spark plug wires that have been on there since possibly when that thing rolled off the assembly line, probably the spark plugs too.

Usually misfire at idle and hard to start means gap gone wide due to erosion, among other things...

Replace spark plugs, gap .030- .035 and

Replace spark plug wires, I would recommend using 8mm ones.

 

That's if you can't remember when they were last done, or if they were done more than 4 years / 50k miles ago.

Start there, then we move on to other things.

 

On 6/2/2019 at 3:28 AM, sefiroxx said:

On 5/30/2019 at 3:48 PM, FourthandShort said:

Thank you for the feedback.  The scanner is telling me its cylinder number 4 with the misfires.  Should I just change them all?  
 
Also the scanner isn't pulling an codes, it tells me no codes found.  The lights come on and then after a few seconds, everything clears up. 

If you are running the original plugs, you might as well change all of them. Check cyl 4 plug for carbon build up - an injector may be stuck open. Use a timing light to see if it is firing. If not swap the coils with another cyl to see if the misfire moves. If yes, a new coil is needed, if not, a new wire is needed

 

To everyone who has responded, I wanted to say thank you.  

 

I usually perform most of my own maintenance and the truck only gets driven about 10k miles a year.  I don't believe I remember when I last changed the plugs so that is a great start and is exactly what I was thinking it might be.  I asked as I had an engine oil leak recently and researched on here that it was more than likely the main seal which is known for wearing out on these types of vehicles.  I really was hoping this was a similar issue where a rough start was something common on this truck for a specific reason.  It seems that old shitty plugs and wires are a common cause for this.  

 

I was also trying to see if anyone else could help narrow it down as I only experience the issue for about 30 seconds on startup after the truck has sat for an extended period of time.  If I drive the vehicle for a short time, and come out to start it up, it fires up perfectly without any issue.  Its not an easily replicated issue unless I leave it sitting for a day or so.  I assumed bad plugs would effect the engine continuously and would be a problem each time the vehicle started, instead of only happening after sitting a while.  I also thought a faulty injector would show symptoms consistently rather than sporadically.  

 

It seems as it might be related to the AFM as the #4 Cyl is the one which controls this and was the only cylinder misfiring when I hooked up the computer.  All other look good. 

 

I was considering running some seafoam through the engine as well to try and clean anything out, however I was unsure if additives could cause additional problems.  

 

Thanks again for the help on this.  I am looking at selling the truck to upgrade and don't want to hand someone else a bunch of problems. 

 

Thanks again to anyone who has contributed, I took it to the shop and they were even clueless to what the problem could be and also suggested swapping plugs, wires, and coils.