Running rough on Start up

I have a 2000 jetta tdi with 440,000 miles original engine and turbo. Third slushbox. I need some advice. When I go to start it up in the morning or anytime after sitting for about 8 hours it starts and runs real rough for about 10-15 seconds regardless if its cold or not. I started it this morning and it ran rough for about 30 seconds then smoothed out. It was about 45 degress this morning so it ran rough for longer than normal.

My question is what is causing this? Can my timing be off in vag-com? I have vag-com but not real sure how to adjust this. Can the injectors be going bad? They are the original injectors I believe. Would it be worth the while replacing them? If so do I go bigger or just get something similar? I drive it 100 miles a day so really looking for good gas mileage. Do injectors go bad after so long? Any help is greatly appreciated.

Sounds like you've got an air leak in the fuel system.

Injectors do go bad, injection timing could be too retarded, glow plugs not working.