Tell him to test your coil. If he does not want to buy one they are about $100 -150. I had a similar issue bogging down on hard acceleration from start and slightly rough idle but otherwise fine.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)