Have your alternator and battery checked. I know that sounds kind of simple but sometimes a weak alternator can cause a rough idle. Although it would be weird for it to only do it when it is at operating temp. I would test for a draw in the electrical system if those both pass.
The MAP shouldn't change anything if unplugged. The MAF will do something. I would say that it would be a good idea to unplug that and if nothing changes it might be faulty. Are there any codes? Passed or current?
I don't think that it would be a head gasket as it would have a lot more issues than just a rough idle.

 

AC Delco spark plugs, check all vacuum lines for cracks, leaks or poor fitting.; run gas line anti-freeze to clear up any moisture that may be in the fuel system.

 

I did not see any discussion on checking the idle air circuit or idle air control valve. There might be some low hanging fruit there. I have never had a problem with it but I have read where removing and cleaning carbon from the IAC valve is doable. Or looking up some electrical specs and seeing if it (IAC valve) is receiving the proper signal. With the throttle plate open when above idle it would mask any problem above idle speed and a idle setting from the IAC valve stepper motor may be fine when warm but not when cold.

 

That's because there is no IAC on his truck. :lol:

It's a fly by wire and all controlled by the throttle body, which he has already cleaned.

 

Thank you all for the quick replies!

I will stop by a parts place today and ask them to do a test on the Alternator. I have noticed that it dips below the 14V mark on the dash gauge more often than I would like. I thought it might be the battery, but it appears to be new. I'm probably going to replace it with a sealed AGM regardless in the near future.

I did not test the MAF with the engine running. I'll try that at the parts place too (engine will be nice and warm at that point).

I only mention the head gasket potential issue because if it is bad then coolant may be getting into cylinder 7 and causing a misfire. although a misfire would show up on the dash.

Enforcer: you bring some good points on the vacuum lines. I attempted to trace them last night but it was just too dark. The sun is out today so I'll give that a go. In terms of the ACD plugs; everyone's post i read on all the big full size forums said I should run the Iridium plugs from ACD. I 100% want to run them but from what I found ACD does not specify Iridium plugs for my truck any longer. They have the Platinum set which I was going to go with however, given the push for the Iridium I went Bosch. I did do a little scouting through a few other models (Tahoe, Yukon, etc) to see if they are specified there. But what i've found is ACD doesn't make the .040" gapped iridium plugs. I'm happy to be proven wrong here.

Correct, there is no IAC on the throttle body. There is a little unit on the side (name escapes me) that I did remove and clean independent of the TB just for good measure.

I'll run a can of moister remover starting today.

As an aside to the rough idle. I've noticed this engine doesn't warm up all the quickly. I live about 8 miles from my office and given the temps right now (20 degrees) it barely makes it to operating temp by the time i pull in the parking lot. I've thought about blocking off a portion with cardboard just to bring it to temp faster.

 

Have your alternator and battery checked. I know that sounds kind of simple but sometimes a weak alternator can cause a rough idle. Although it would be weird for it to only do it when it is at operating temp. I would test for a draw in the electrical system if those both pass.
The MAP shouldn't change anything if unplugged. The MAF will do something. I would say that it would be a good idea to unplug that and if nothing changes it might be faulty. Are there any codes? Passed or current?
I don't think that it would be a head gasket as it would have a lot more issues than just a rough idle.

I have a 2013 2500hd 6.0 litre doing the same thing no codes been to 6 garages and 3 gm dealers I got answers from I don't know to it needs a new engine so I replaced every sensor new variable valve timing kit new coils new spark plugs new spark plug wires new O2 sensors all the catalytic converters replaced that wasn't cheap new ECM oil change there's no oil in the anti freeze no anti freeze in the oil I actually pulled all the covering off the wire harness checked every wire all good no bare spots no melted wires every wire going into the connectors all good fuse box everything there great condition all fuses and relays are fine start it up runs like the day it was built as it approaches operating temperature it starts to get a slight miss then it starts backfiring the motor starts jerking popping spitting sputtering and when it hits operating temperature it stalls I understand what you are going through if anyone's got an idea please let me know I'm baffled it's a shame this truck is in beautiful shape other than the engine oh also every ground on it has been cleaned or replaced I read that grounds were a common problem with these trucks not this one

 

depending on the timing of this snow storm I may try to do a compression test. It may not tell me much about the rough idle, but i'd like to know if there are any other compression related issues.

 

Did you clean the ground under the driver's door .it controls the fuel pump

 

I would be looking at the temp sending unit that signals the ECM. The ECM may think the engine is not up to temp therefore feeding it to much fuel.

 

Seems to be updates regarding spark plugs through various references.
Vehicle: 2005 GMC Sierra 1500 5.3L V8 VIN:B,T
Sierra 1500, 1999-2010
2005 5.3L V8 VIN:T

Platinum Spark Plug
Part Number: 41-962
Product Notes:
Double Platinum Spark Plug
All; OE; Gap .040; VIN: B, Eng Code: L33*; VIN: T, Eng Code: LM7*; VIN: Z, Eng Code: L59*
Per Vehicle: 8; Years: 1999-2006

 

Scrap the Bosch plugs and put the proper AC Delco 41-110 in it.

These engines don't like Bosch plugs, and they are utter garbage in my opinion.

 

Another thing to check is live O2 readings and the fuel trims with a scan tool. Coworker's 04 had a bad O2 sensor on the driver's side that when it would get to closed loop it would pig out on fuel on that bank, which would make it run poorly. Eventually it got bad enough that it was fouling plugs and misfiring, but still was not quite bad enough for the ECU to notice that the sensor was the fault. Checked the readings, saw the terrible O2 readouts, replaced the O2 sensor, cleaned the plugs up, and it has purred ever since.

 

O2 sensors are something I always overlook. I'm going to see if I can find my OBD reader and run the live scan on this.

I have a generic software for reading OBD 2 systems. Does anyone have a recommendation for a more GM specific software? Preferably something that can interface with the body computer as well.

 

Scrap the Bosch plugs and put the proper AC Delco 41-110 in it.

These engines don't like Bosch plugs, and they are utter garbage in my opinion.

How about NGK Iridiums? Are they any good. Replaced mine with them for a misfire issue

 

O2 sensors are something I always overlook. I'm going to see if I can find my OBD reader and run the live scan on this.

I have a generic software for reading OBD 2 systems. Does anyone have a recommendation for a more GM specific software? Preferably something that can interface with the body computer as well.

I just use Torque on my Android, with a bluetooth OBDII adapter. Only cost me about 30 bucks total for everything and it works great. I did buy Car Gauge Pro as well as that will scan for faults in ABS/BCM/TCCM/etc but it isn't as polished or user friendly as Torque for what I use the most, but having both is quite handy. Still under $40 for both apps and the adapter.

 

If you put your foot on the pedal at idle, and raise the rpms by 50, then 50 again, and again...does that make it better or worse? Better, have the ECM changed to idle at the smooth speed, and spend some time cleaning your top end and intake track. seafoam works too sorta. If it doesn't get better, could be a host of things but my bet would be engine mounts as long as everything else appears to operate regualry

 

Scrap the Bosch plugs and put the proper AC Delco 41-110 in it.

These engines don't like Bosch plugs, and they are utter garbage in my opinion.

How about NGK Iridiums? Are they any good. Replaced mine with them for a misfire issue

NGKs are great plugs. I run them in my VW b/c they are OEM. I don't know if I'd want to put them in a GM engine. That's just my $.02.

 

If you put your foot on the pedal at idle, and raise the rpms by 50, then 50 again, and again...does that make it better or worse? Better, have the ECM changed to idle at the smooth speed, and spend some time cleaning your top end and intake track. seafoam works too sorta. If it doesn't get better, could be a host of things but my bet would be engine mounts as long as everything else appears to operate regualry

If I give it any gas it's smooth as butter. Drives great, holds 80 on the freeway for days. But at a stop light/sign it will shake.

I have done a Seafoam through the tank, full can. I have a half can in the oil right now will be changing the oil this weekend. The other half I let get sucked into the vacuum line and sit for 15 minutes. Didn't help the shake at all sadly.

I still need to check the O2 sensors, i haven't had the opportunity to find my OBD2 reader yet. I will change the motor mounts but I'm going to wait on those until it's a bit warmer. Sadly I don't have a shed to work in.

I'm also going to replace the intake gaskets over new years weekend. I would make sense they would expand with the heat and allow air to pass the wrong way.

 

all good things to check. rough running at idle if you can verify your fuel pressure is good, points to an air issue or a wear parts failure like mounts.

What about your serp belt, pulleys and tensioner? I didnt read through the whole post if that was already mentioned

 

Belt and pulleys don't alarm me, i will probably replace them because the idler pulley is looking a little too rusty for my taste. No noises though.

I did check the fuel pressure. I believe it was 57psi key on engine off and 65ish psi at idle.

 

I would say that the NGK Plug are definitely better for the GM's. If you don't hear anything from the pulleys I wouldn't worry about it. I personally don't like any of the programs that you use your phone to read or data log from the vehicles. They usually are not as useful or accurate. If you have an actual hand held that would be more useful. I have a very expensive one due to my line of work but you don't really need a top of the line scanner. Just a cheap one that can data log. Anyway, I would check for the o2 ratios and pay close attention to them to see if there is anything that shouldn't be the way it is. I would also pay attention to the MAF and MAP sensors to see what they are reading. The problem is most likely going to be an o2 sensor though.

 

NGK over the ACDelcos?

I have a plug in ELM327 style unit. I know it'll give me O2 readings on my VW. I'm hoping it's a similar enough protocol to read the GM's computer. VW is pre Canbus so I don't know how well that'll work. It also requires my Windows laptop which is currently dead. I may install bootcamp on my mac if I can find my license code.

 

all good things to check. rough running at idle if you can verify your fuel pressure is good, points to an air issue or a wear parts failure like mounts.

What about your serp belt, pulleys and tensioner? I didnt read through the whole post if that was already mentioned

im jumping in a little late but i have very! very close symptoms mine shakes everything has been swapped fuel trims o2s and compression are all equal and mint.. would bad mounts cause exhaust to sound off also?

 

Engine mounts wouldn't cause a change in the exhaust note just by being bad. If you've noticed a change and suspect the engine mounts my conclusion would be the bad engine mounts allowed the exhaust system to crack somewhere.

 

Doubt it just been through everything i got the same issues as him except even at cold temp as soon as it idles down.. Im 99% sure its torque converter now due to the history of it having muddy water for 2 months and losing over drive till i flushed it.. As for engine all i have left is knock sensors that looked new and good cam sensor ect sensor and pcm..

 

My exhaust note hasn't changed at all with the rough idle. I just feel it shaking from the driver's seat.

If you're getting the rough idle at cold temp I would look at the intake manifold gaskets. Those seem to be the common problem with the 5.3s rough idle. I made this post because everyone was saying check the gaskets but mine are fine. no vacuum leak according to my gauge and the smoke test.

 

Have any live scan data yet? Fuel trims for both banks with rpm, the both upstream sensors with Rpm. Need idle and around 2500 rpm data.