rough idle/vibration

[mjwills]

Hi all - I'm new to the forum and appreciate any help. I just came out of a 2005 ESV into a 2011 Yukon XL 2500. Even though they both had the 6.0L - are there differences? I know the tranny is different and I am still learning shift patterns, etc.

Upon start up it sticks around 1200 and after a minute will creep down to 600. Is that normal?

Sometimes at lights or in park there is a rough idle - bounces up or down 50-100rpm. I cleaned the throttle body and put in a K&N filter and waiting to see if that helped out enough. No engine lights are on so I assume it is not miss firing. When it is in park and doing this I opened the hood and the trans dip stick was shaking really bad from the vibration.

Any other things to look at?

Thanks!

 

[mentalattica]

I'm not as knowledgeable as most of the folks on here but as far as when you're starting the engine that sounds normal to me. All of my vehicles do that.

As far as the rough idle how many miles are on it? Have you taken a look at the plugs? If not I'd pull a couple and see what they look like, also check the wires. I've had a few vehicles that were missing and not throwing any codes, in fact my Saturn is currently doing that.

If the plugs and wires look good maybe there's a vacuum leak somewhere? You can also try running some Seafoam (or something of the likes) through it too.

Maybe someone will chime in with better info, but the plugs and wires is where I'd start.

 

[mjwills]

Thanks for the response. There is 80k on it.

 

[CrashTestDummy]

The behavior your seeing at startup is normal. The idle hunting like that is not. You may want to have a dealer check that out, there may be a sensor that's not working correctly, or the throttle positioning sensor (TPS) may be out of adjustment.

 

[mjwills]

Taking it to dealer Monday. There are really 2 vibrations going on. One at idle where it's fine and then you hear a click and then a surge comes through column, dash and seat. The other is one that I feel only around 1800 RPM - in the feet and column. This may be more of a droan?? I can drive through it, but after every shift it goes back to that point and at around 70mph its at 1800.

Do engine/trans mounts go bad?

 

[GM Customer Service]

Hello mjwills,

Our apologies to hear of the concerns you are experiencing with your 2011 GMC Yukon. We understand you'll be taking it in to the dealership on Monday, please keep us updated on your visit!

Regards,

Andraya
GM Customer Care

 

[rockenthebowtie]

Is it with the AC on only or on or off it kinda sounds what your describing like the AC compressor engaging but thats not normal you may have a AC COMPRESSOR starting to fail and or seize up causing the idle drop and at 1800 rpm at 70 mph

 

[mjwills]

Hi all - well no luck and its been to 3 dealers. They see it and feel it but are stumped on a fix. One dealer put a dampner behind the right side cat and the other put a new clamp on the exhaust and realigned it. Since there are no codes they keep thinking it is in the exhaust. Both say it could be a engine/trans mount but not 100% confident. I'm at a loss and its frustrating that the dealer can't solve it. Thoughts on next steps?

 

[mjwills]

Talked more with dealer. They said if it were them, a new exhaust is the fix. Would a cat back system work? Any other thoughts?

 

[992dr]

What's amazing to me is that these so-called certified technicians can't do there jobs.
Isn't diagnosing problems a part of there cert? And yet no one can find the problem. I feel your pain Mark. I've been going through some very similar issue myself.

You CAN have a misfire without throwing any codes. In fact you can have multiple misfires. That is more than likely your issue with the rough idle. This is my issue.

As silly as it sounds, yes motor and trans mounts do fail and it seems to be more common than not.

Check your u-joints and yoke to.

edit I find it very hard time believe its the exhaust. Check your u-joints and yoke.