Personally, i don't believe the Penrite Oil is the issue at all. Even if it wasn't a 504/507 approved it would not cause the issues that your having. Neither would the engine flush or injector cleaner IMHO.

The engine flush used in your service goes in the old engine oil before replacement and the fuel injector cleaner goes in the fuel tank. Neither of those products would have made a difference to the carbon buildup that i'm referring to.

What i'm referring to the intake throttle body that is after the EGR valve on the air intake system. It is known to get carbon buildup and cause issues. The issue that you describe is exactly the same that i have experienced. i don;t recall getting a code with issue either as it was intermittent but alot more noticeable when the car engine was cold.

If read this post here on vwatercooled specifically post #6

That is exactly were i had carbon build up in the intake system which caused my issues.

I would start there, even if your EGR was replaced last year and they never cleaned the throttle body, it will still be full of carbon as it is post EGR valve.

Hope that helps and let us know how you go.