i've got about 4,500 miles left from a 100,000 mile warranty first off. so anyways, i get off work at about midnight, get in my truck to leave and right off it starts to idle funny, like a small misfire. tired and hungry i opt for going home instead of taking a peak under the hood. i get on the road, the stupid service engine soon light keeps blinking at me and my engine feels like a good amount of pistons are misfiring. 1 minute later, right when i'm bout to turn around and go back to work to see what's up, it stops shuttering. get stopped at a light, service engine soon light is still on speed. stop light turns green, i go, and it all starts over again. one more light, same thing. get on the freeway (and man was this thing a turd trying to get on) and slowly climb to 65, then the light goes off. turns out, when i'm at a steady speed, everything was fine. so i make it home fine, and try to see if i can get the misfire to happen again, and nothing. maybe because it was warmed up enough to run right? i don't know. well i opened the hood, everything seemed fine, but the radiator hose, it wasn't as hot as usual and could easily pinch the hose, it didn't have as much pressure built up. so what's up? anybody? sorry for the length too, kinda concerned.

 

It could be fouled plugs....that will definitely cause misfires, it could also be a bad plug wire or clogged injectors (not very likely though), try changing the plugs and see what happens

 

Get that thing in the shop ASAP while you are under warranty.

 

Bumper to bumper 100K warranty? If so, make a list of every single thing that you have an issue with. Have that list repaired under warranty. When you go to pick it up, check off every item on your list. If something wasn't fixed to your satisfaction, leave it with them to complete. You payed for the warranty, get your money's worth out of it. In 4000 miles, its coming out of your pocket.

 

I believe my '02 5.3 Avalanche did the same thing, if not real similar.

I started it up one 45*F rainy morning at my g/f's house, and it didn't catch right away. Turned it over again, and it didn't want to stay running - sputtered out. Third time I got it lit, but it was running HORRIBLE. Like you said, it was missing 2-4 cylinders. The truck was shaking pretty bad. The engine light came on. It wouldn't stay running without 1/4 to 1/2 throttle.

I got under the hood to see what's up. She has a real bad mice problem with vehicles at her house, because her neighbors have a horse barn about 100 feet away from her driveway. I have to clean mice-nests out of her engine and airbox once every few months. I thought for sure they found something of interest, under my hood. But there was nothing.

I played with the throttle to "clean it out", and I only got it running on 6 or 7 cylinders. It was backfiring and farting pretty bad. By now my girlfriend in the house is giving me dirty looks, wondering WTF I'm doing out there, so I go to tell her the truck's acting funny. I go back out, and the thing was idling smooth as ever.

Drove around, and it was fine. The light I got was just a generic random missfire code. The problem never came back for the next 5 months I had the truck.

I really can't even GUESS what the problem might have been... I can only offer the possiblity that it was a fluke thing, and won't come back.

 

If you have an EGR valve, that could be the culprit.

 

alright, well i finally took it to the dealer, with a list of problems: fuel gauge going crazy, engine crapping out as descibed above, and pinging. they hooked it up to the tech2 and no trouble codes. the fuel gauge was because of the fuel sending unit, got that replaced. engine taking a dump on me was inconclusive. and the pinging, get this...they said that pinging is normal for these trucks and i should not be concerned . luckily my hypertech takes care of that problem for me, but with no tune, i can't go above 4000rpms without detonation. when will big businesses learn that honesty and loyalty is what keeps a customer. lucky for GM they've got the better truck compared to competition or else bye bye. i mean seriously, throwing me a line saying it's normal, i think the guy is just looking out for his job, knowing that more deception equals more business to come later on.

 

when is the last time you had your o2 sensors checked?

 

thats my vote too, if they are slow to come online you will get those symptoms and with nearly 100k it is time for new ones anyways.

i had that same condition and it never set a code, other than a missfire code and i could hear and feel that.

 

O2 sensors have never been changed...how much do they run for anyways?