Dirty intake valves?

[fiziksgeek]

2014 Silverado CCSB with 5.3, all stock. 70K miles

Several months ago I got a check engine light. Brought it to the dealer as it was due for an oil change, they said "misfire" but could find no obvious cause. Its continues to happen sometimes twice a week, sometimes not at all for a month. At my last oil change I had them change the plugs and wires, relatively inexpensive thing to try, still happens. Battery died a couple month ago, replaced it, still get the light occasionally.

Within the last month developed a new symptom. When I shut it off, the engine will sometimes sputter a bit, even after the key is pulled out. Only for a second or two before dying. 

Is this all consistent with dirty intake valves on a direct injection engine?

[Lsgun1]

If the intake valve was that carboned up it should misfire all the time. Could be an injector acting up.

[Jacoby]

Start with the cheap remedies first. Seafoam in a couple tanks of gas. If you’re up to it Seafoam the intake. See if those clear it up at all

[truckguy82]

I have trouble believing the dealer had access to a cel and just threw their hands in the air  “no clue man sorry”

[TRKLGND]

11 hours ago, Jacoby said:

Start with the cheap remedies first. Seafoam in a couple tanks of gas. If you’re up to it Seafoam the intake. See if those clear it up at all

Seafoam or any other fuel additive will do nothing to clean the valves on a DI engine.  The fuel is not sprayed onto the intake valve.

[Jacoby]

4 minutes ago, paracutin said:

Seafoam or any other fuel additive will do nothing to clean the valves on a DI engine.  The fuel is not sprayed onto the intake valve.

I’m well aware of that. Someone else said maybe an injector issue. What seafoam will do is help with a clogged injector if that is the problem. 

[TRKLGND]

22 minutes ago, Jacoby said:

I’m well aware of that. Someone else said maybe an injector issue. What seafoam will do is help with a clogged injector if that is the problem. 

The OP is titled "Dirty Intake Valves?"

[Jacoby]

20 hours ago, Lsgun1 said:

If the intake valve was that carboned up it should misfire all the time. Could be an injector acting up.

 

1 minute ago, paracutin said:

The OP is titled "Dirty Intake Valves?"

Dude I get that. I was merely adding onto the suggestion above. 

 

Since you you didn’t seem to notice I also suggested a DI cleaning which addresses the valves directly. 

 

 

[L86 All Terrain]

Did it just say general misfire, or did it tell them what cylinder? Even my $120 scan tool will tell me which cylinder is having a misfire. Even when I had my old 1998 K1500, did plugs on it once and one of the new plugs was defective. Scan tool tells me cylinder 7 misfire, change cylinder 7 plug, good to go. I cant see a dirty intake/valves causing a complete misfire, more likely to lose power and suck back the gas than anything. It would have to be very dirty to cause a misfire, like dirty enough to not flow the right amount of air for the amount of fuel supplied by the injector, which would be seriously gummed up intake/valves. Injector would be my guess, you did plugs so those are good and new. Maybe a coil slowly on its way out?