RepairPal Certified shops can diagnose and repair your 2003 Volkswagen Jetta. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Bring it by my shop in Scarborough and I will give you a free engine diagnostic,
Without knowing what codes are there it is hard to diagnose although I know of many common problems, such as plugging of the intake with soot and such!