I just joined this site and found your post. I am having the same problem. Did you ever get any help?

 

Well, I guess the car is suppose to do this. When the car isn't moving, the computer raises the rpm's to keep the a/c cold. It's stupid.... I hate it.

 

Same thing happened to me yesterday. I have a 2008 3.6L 4motion with 98000km. It happened after a short ride on the highway.
Weird feeling.

 

Mine has also done this a couple of times now. It seems to only do it if the A/C is on. Outside temp doesn't seem to make a difference. I had the dealer look at it but they (of course) couldn't replicate it. I've found that if I turn the A/C off, out the car in neutral and then rev the motor above 2,000 rpm's it will then idle correctly. Strange...

 

Brought the car to the stealership (for an unrelated "check engine"). Cost me $200 for diagnostics alone! It turns out it's the Throttle Valve. It jams sometimes, preventing the rev to go back to normal. The part costs 400$... :banghead: In the meantime, when it happens, I shift to neutral and rev up the engine, as mentionned by cpark.

 

When in doubt clean throttle body
Well, I did. It still have surges.
Btw it has nothing to do with the A/C. I've been driving without any A/C for a week. My engine is still randomly surging at idle.
I have to shut the engine down to go back to a normal 600rpm.
The Stealership tells me it's a short in the Throttle Body Valve, but I doubt it.

 

up

 

Never had a 3.6 but cleaning throttle body also means delicately cleaning the flap as well, like where it meets body. Don't use Carbon Tet. Fit a new gasket. And then re-adaption in VCDS. I've got a 2L tFSI so if yours's got same system...

 

I have had similar idle surge at stops with my 2.0T. Realized my big foot was touching the gas pedal while applying the brake.

 

Went back to the stealership. No CEL, no codes. Still, they could replicate it. On a hunch, they cleaned every ground connector in the engine (except for the main battery cable that runs from the trunk to the engine). Cost me 300$, and it's still acting crazy.

I've noticed that every time I turn off the engine while it's (abnormally) revving at 1100rpm, I can hear the fan spin down.

Any suggestions as to why it is revving up?
Sometimes, I'm just waiting at a red light, and I can see the needle starting to go up very slowly from 600 to 900 for no reason. It's as if the car was possessed!

Is there an ISV on the 3.6L?