2002 1.8T...no codes but problems

No check engine light..
Hardly starts, very low power
For the first minute before the big turbo boost runs VERY ROUGH.
If the A/C is on, it won't start...

Seems almost like the lights dim as well??

VW dealer has already changed the plugs, nothing happened.

Don't want to spend thousands for them to guess...

Any ideas....???

Checked the battery or alternator... sounds like they could be shot.