Gentlemen, first off, thanks for all that offered suggestions. Me and a buddy, who is also a FANTASTIC mechanic, spent over 5 hours in his shop trying to figure this damn thing out.

• We swapped to the OEM MAF (OEM sensor as well) - nothing
• Checked the new O-ring we installed, reseated it - nothing
• We swapped to the V8 MAF sensor - nothing
• Carb cleaner around the TB - nothing
• Propane trick - nothing
• Used a smoke machine to test for leaks - nothing
• Used a Verus (snap-on) diagnostic computer and made the ECU essentially relearn the idle throttle positioning - nothing
• swapped to 74mm TB and V8 MAF - nothing

Since none of our tests found any leaks, we figured all was snug and tight, but just for ***** and giggles, we decided to RTV the TB. Sure enough, it is now running perfectly.

It was a vaccuum leak that was not evident under normal running conditions, only under extreme acceleration. I drove around with the snap-on diagnostic machine in the car and it did not even find the issue.

Long story short, even though there is a factory O-ring and it appears to be sealed, it probably is not, try an even bead of RTV, as others have suggested, because there is apparently no other way of testing for this, except to just seal it.

Wish I would have done it from the start, but silly me, I figured OEM mercedes parts would fit together well enough to not cause leaks, and if there were leaks, I would have thought our normal diagnostic procedures would have found it like in all other cars I have worked on.

Either way, just glad it is done and running perfectly before the Dragon