Bizarre surging while in Drive stopped

[WestLinnYukon]

Hi there, I have a 2004 Yukon XL 5.3 auto 4x4. At a stop light, in drive with brake applied it surges. Thought it was missing but it’s not. If I shift into neutral it stops. Never had an issues before. I recently started using Auto 4x4 for the first time in the ice, but it is doing this in 2wd.

Is some mechanism of the auto 4x4 stuck on?

Could a ujoint be so bad and loose the transmission thinks the vehicle is starting to move even though it isn’t.

The surging is rapid and really feels like missing, but again as soon as I am in neutral it purrs like a kitten, and also runs great once moving.

Thanks in advance!!

 

[Doubeleive]

Hi there, I have a 2004 Yukon XL 5.3 auto 4x4. At a stop light, in drive with brake applied it surges. Thought it was missing but it’s not. If I shift into neutral it stops. Never had an issues before. I recently started using Auto 4x4 for the first time in the ice, but it is doing this in 2wd.

Is some mechanism of the auto 4x4 stuck on?

Could a ujoint be so bad and loose the transmission thinks the vehicle is starting to move even though it isn’t.

The surging is rapid and really feels like missing, but again as soon as I am in neutral it purrs like a kitten, and also runs great once moving.

Thanks in advance!!

I would look at the fuel pressure with a guage and see if the fuel pump is getting whacky
surging is typically the fuel pump but could be other things but it's a good place to start and rule it in or out.
the reason you may notice it in gear versus not in nuetral is engine load vs no engine load.
you may also want to take a look at the throttle body has it been cleaned? any kind of intake service performed?

 

[WestLinnYukon]

Well, it turned out to be a cracked spark-plug on cylinder 6. When I got home I used auto doctor and there was a pending code that was not there before. A week ago I was installing a manifold clamp (don't judge) in the area and when I "moved" the dipstick tube out of the way I bet I levered it against the plug accidentally cracking the porcelain. Glad it was something simple.

 

[Doubeleive]

Well, it turned out to be a cracked spark-plug on cylinder 6. When I got home I used auto doctor and there was a pending code that was not there before. A week ago I was installing a manifold clamp (don't judge) in the area and when I "moved" the dipstick tube out of the way I bet I levered it against the plug accidentally cracking the porcelain. Glad it was something simple.

lot cheaper than a fuel pump!