Clean the TB and check for vacuum leaks as stated.
If this does not cure the problem I'd say with CONFIDENCE it's the tune.

I went through the same problem in the 06GT and mine was tune related.

 

Today I bought some TB cleaner (CRC I believe) and gave the TB a thorough cleaning. It was disgustingly dirty but I noticed a very significant difference after cleaning it. Idle issues were gone, and the throttle response was much improved. Problem solved

 

Yeah, baby! I'm sure that's a relief.

 

Big time!

 

Here's some pics showing how gross it was...

Before


After

 

That's why I have a oil catch can installed.....imagine the intake contamination.

 

Alec,

I've yet to pull my TB off. Did you reuse the gasket?

 

There is no gasket. There is a ring that is built into the plenum, im assuming they use that instead of the gasket now. Either way i removed mine numerous times and the only thing i did is clean around the rubber ring, never had a problem.

 

^^ yep

 

Excellent.