Stalling at idle issue. Need help.

[Turbodent]

Need some help with the wife’s truck. 
 

To start off, it’s a 2012 gmc sierra 5.3 with 460,****** KM. Been a drop dead reliable truck. That’s been in her family since new. 
 

recently it would fire up idle for a minute or so then die, only at idle if you’re driving or revinf the engine up it doesn’t do it.  Got some misfire codes on the drive home the first time it happened.
 

Her dad wasn’t sure if it ever got plugs so I threw a set of plugs at it and it ran way better. Gave the truck back to the wife and it died at a stop light on her drive home from work. Now zero codes. I looked at it went through the entire truck no smoking gun.  So is started driving it daily for a few days with my scan tool on it. Had it happen to me a few times fuel pressure stays around 52 psi even when it would die. For a u0101 code the other day. TCM wiring looks good. All the grounds are in good shape.
no vacuum leaks or anything like that. 
 

couple mechanic buddy’s of mine are stumped too.
 

what should I check?  

[CamGTP]

That's a tough one to figure out without probably scoping the crank sensor or watching it on a live data scan tool. Possible that it's just dropping out for a split second and that is enough at idle to stall the engine. This is only a guess of course.

 

Also I'd make sure the throttle blade was really clean, a dirty throttle body could cause a stall too.

[Turbodent]

4 hours ago, CamGTP said:

That's a tough one to figure out without probably scoping the crank sensor or watching it on a live data scan tool. Possible that it's just dropping out for a split second and that is enough at idle to stall the engine. This is only a guess of course.

 

Also I'd make sure the throttle blade was really clean, a dirty throttle body could cause a stall too.

I’ve watched the rpm signal on my scan tool and it shows constant rpm and a decline to zero when it stalls. Doesn’t go to zero and back, before the stall. 

[kickass audio]

4 hours ago, CamGTP said:

That's a tough one to figure out without probably scoping the crank sensor or watching it on a live data scan tool. Possible that it's just dropping out for a split second and that is enough at idle to stall the engine. This is only a guess of course.

 

Also I'd make sure the throttle blade was really clean, a dirty throttle body could cause a stall too.

I am also with you on the throttle body being cleaned. I've had a gummed up throttle blade on a friends truck that made it idle like crap and almost act like it was close to stalling itself out.

 

Do you have a higher end scan tool to check the misfire count on each cylinder? Maybe that can help you track it down to a specific side of the engine or the cylinder that is acting up and maybe you have bad plug wires or a bad ignition coil that is acting up at idle.

 

With how you mention it seems to have run better with new plugs you might also have 1 or more failing ignition coils from having worn out plugs that stress out the coil and make it work harder and can cause it to fail.

[Turbodent]

So update to this, swapped out the throttle body and it got a lot better until tonight, only code I could read is. P0300. Going to get my good scanner on it in the morning. Any ideas? I saw a video where the o2 were causing the code. 

[asilverblazer]

O2 sensors are everyone's favorite scapegoat for anything wrong. Don't replace parts without a proper diagnosis. Try to get miss fire counts to determine if you are really looking at random miss fires or if there are a few problematic cylinders.

[thx1138v2]

I had a similar problem with the engine dying with no rhyme or reason. It turned out to be a crankshaft position sensor. It didn't throw any codes either. This was on a 2007 GMC 4.3L and I ended up loading the parts cannon and finally found it that way.